diff --git a/src/applications/feed/PhabricatorFeedStoryPublisher.php b/src/applications/feed/PhabricatorFeedStoryPublisher.php
index 9770c89db9..7cb3d33884 100644
--- a/src/applications/feed/PhabricatorFeedStoryPublisher.php
+++ b/src/applications/feed/PhabricatorFeedStoryPublisher.php
@@ -1,227 +1,276 @@
 <?php
 
 final class PhabricatorFeedStoryPublisher {
 
   private $relatedPHIDs;
   private $storyType;
   private $storyData;
   private $storyTime;
   private $storyAuthorPHID;
   private $primaryObjectPHID;
   private $subscribedPHIDs = array();
   private $mailRecipientPHIDs = array();
   private $notifyAuthor;
+  private $mailTags = array();
 
+  public function setMailTags(array $mail_tags) {
+    $this->mailTags = $mail_tags;
+    return $this;
+  }
+
+  public function getMailTags() {
+    return $this->mailTags;
+  }
 
   public function setNotifyAuthor($notify_author) {
     $this->notifyAuthor = $notify_author;
     return $this;
   }
 
   public function getNotifyAuthor() {
     return $this->notifyAuthor;
   }
 
   public function setRelatedPHIDs(array $phids) {
     $this->relatedPHIDs = $phids;
     return $this;
   }
 
   public function setSubscribedPHIDs(array $phids) {
     $this->subscribedPHIDs = $phids;
     return $this;
   }
 
   public function setPrimaryObjectPHID($phid) {
     $this->primaryObjectPHID = $phid;
     return $this;
   }
 
   public function setStoryType($story_type) {
     $this->storyType = $story_type;
     return $this;
   }
 
   public function setStoryData(array $data) {
     $this->storyData = $data;
     return $this;
   }
 
   public function setStoryTime($time) {
     $this->storyTime = $time;
     return $this;
   }
 
   public function setStoryAuthorPHID($phid) {
     $this->storyAuthorPHID = $phid;
     return $this;
   }
 
   public function setMailRecipientPHIDs(array $phids) {
     $this->mailRecipientPHIDs = $phids;
     return $this;
   }
 
   public function publish() {
     $class = $this->storyType;
     if (!$class) {
       throw new Exception('Call setStoryType() before publishing!');
     }
 
     if (!class_exists($class)) {
       throw new Exception(
         "Story type must be a valid class name and must subclass ".
         "PhabricatorFeedStory. ".
         "'{$class}' is not a loadable class.");
     }
 
     if (!is_subclass_of($class, 'PhabricatorFeedStory')) {
       throw new Exception(
         "Story type must be a valid class name and must subclass ".
         "PhabricatorFeedStory. ".
         "'{$class}' is not a subclass of PhabricatorFeedStory.");
     }
 
     $chrono_key = $this->generateChronologicalKey();
 
     $story = new PhabricatorFeedStoryData();
     $story->setStoryType($this->storyType);
     $story->setStoryData($this->storyData);
     $story->setAuthorPHID((string)$this->storyAuthorPHID);
     $story->setChronologicalKey($chrono_key);
     $story->save();
 
     if ($this->relatedPHIDs) {
       $ref = new PhabricatorFeedStoryReference();
 
       $sql = array();
       $conn = $ref->establishConnection('w');
       foreach (array_unique($this->relatedPHIDs) as $phid) {
         $sql[] = qsprintf(
           $conn,
           '(%s, %s)',
           $phid,
           $chrono_key);
       }
 
       queryfx(
         $conn,
         'INSERT INTO %T (objectPHID, chronologicalKey) VALUES %Q',
         $ref->getTableName(),
         implode(', ', $sql));
     }
 
-    $this->insertNotifications($chrono_key);
-    $this->sendNotification($chrono_key);
+    $subscribed_phids = $this->subscribedPHIDs;
+    $subscribed_phids = $this->filterSubscribedPHIDs($subscribed_phids);
+    if ($subscribed_phids) {
+      $this->insertNotifications($chrono_key, $subscribed_phids);
+      $this->sendNotification($chrono_key, $subscribed_phids);
+    }
 
     PhabricatorWorker::scheduleTask(
       'FeedPublisherWorker',
       array(
         'key' => $chrono_key,
       ));
 
     return $story;
   }
 
-  private function insertNotifications($chrono_key) {
-    $subscribed_phids = $this->subscribedPHIDs;
-
-    if (!$this->notifyAuthor) {
-      $subscribed_phids = array_diff(
-        $subscribed_phids,
-        array($this->storyAuthorPHID));
-    }
-
-    if (!$subscribed_phids) {
-      return;
-    }
-
+  private function insertNotifications($chrono_key, array $subscribed_phids) {
     if (!$this->primaryObjectPHID) {
       throw new Exception(
         'You must call setPrimaryObjectPHID() if you setSubscribedPHIDs()!');
     }
 
     $notif = new PhabricatorFeedStoryNotification();
     $sql = array();
     $conn = $notif->establishConnection('w');
 
     $will_receive_mail = array_fill_keys($this->mailRecipientPHIDs, true);
 
     foreach (array_unique($subscribed_phids) as $user_phid) {
       if (isset($will_receive_mail[$user_phid])) {
         $mark_read = 1;
       } else {
         $mark_read = 0;
       }
 
       $sql[] = qsprintf(
         $conn,
         '(%s, %s, %s, %d)',
         $this->primaryObjectPHID,
         $user_phid,
         $chrono_key,
         $mark_read);
     }
 
     queryfx(
       $conn,
-      'INSERT INTO %T
-     (primaryObjectPHID, userPHID, chronologicalKey, hasViewed)
-     VALUES %Q',
+      'INSERT INTO %T (primaryObjectPHID, userPHID, chronologicalKey, hasViewed)
+        VALUES %Q',
       $notif->getTableName(),
       implode(', ', $sql));
   }
 
-  private function sendNotification($chrono_key) {
+  private function sendNotification($chrono_key, array $subscribed_phids) {
     $data = array(
       'key'         => (string)$chrono_key,
       'type'        => 'notification',
-      'subscribers' => array_values($this->subscribedPHIDs),
+      'subscribers' => $subscribed_phids,
     );
 
     PhabricatorNotificationClient::tryToPostMessage($data);
   }
 
+  /**
+   * Remove PHIDs who should not receive notifications from a subscriber list.
+   *
+   * @param list<phid> List of potential subscribers.
+   * @return list<phid> List of actual subscribers.
+   */
+  private function filterSubscribedPHIDs(array $phids) {
+    $tags = $this->getMailTags();
+    if ($tags) {
+      $all_prefs = id(new PhabricatorUserPreferences())->loadAllWhere(
+        'userPHID in (%Ls)',
+        $phids);
+      $all_prefs = mpull($all_prefs, null, 'getUserPHID');
+    }
+
+    $pref_default = PhabricatorUserPreferences::MAILTAG_PREFERENCE_EMAIL;
+    $pref_ignore = PhabricatorUserPreferences::MAILTAG_PREFERENCE_IGNORE;
+
+    $keep = array();
+    foreach ($phids as $phid) {
+      if (($phid == $this->storyAuthorPHID) && !$this->getNotifyAuthor()) {
+        continue;
+      }
+
+      if ($tags && isset($all_prefs[$phid])) {
+        $mailtags = $all_prefs[$phid]->getPreference(
+          PhabricatorUserPreferences::PREFERENCE_MAILTAGS,
+          array());
+
+        $notify = false;
+        foreach ($tags as $tag) {
+          // If this is set to "email" or "notify", notify the user.
+          if ((int)idx($mailtags, $tag, $pref_default) != $pref_ignore) {
+            $notify = true;
+            break;
+          }
+        }
+
+        if (!$notify) {
+          continue;
+        }
+      }
+
+      $keep[] = $phid;
+    }
+
+    return array_values(array_unique($keep));
+  }
+
   /**
    * We generate a unique chronological key for each story type because we want
    * to be able to page through the stream with a cursor (i.e., select stories
    * after ID = X) so we can efficiently perform filtering after selecting data,
    * and multiple stories with the same ID make this cumbersome without putting
    * a bunch of logic in the client. We could use the primary key, but that
    * would prevent publishing stories which happened in the past. Since it's
    * potentially useful to do that (e.g., if you're importing another data
    * source) build a unique key for each story which has chronological ordering.
    *
    * @return string A unique, time-ordered key which identifies the story.
    */
   private function generateChronologicalKey() {
     // Use the epoch timestamp for the upper 32 bits of the key. Default to
     // the current time if the story doesn't have an explicit timestamp.
     $time = nonempty($this->storyTime, time());
 
     // Generate a random number for the lower 32 bits of the key.
     $rand = head(unpack('L', Filesystem::readRandomBytes(4)));
 
     // On 32-bit machines, we have to get creative.
     if (PHP_INT_SIZE < 8) {
       // We're on a 32-bit machine.
       if (function_exists('bcadd')) {
         // Try to use the 'bc' extension.
         return bcadd(bcmul($time, bcpow(2, 32)), $rand);
       } else {
         // Do the math in MySQL. TODO: If we formalize a bc dependency, get
         // rid of this.
         $conn_r = id(new PhabricatorFeedStoryData())->establishConnection('r');
         $result = queryfx_one(
           $conn_r,
           'SELECT (%d << 32) + %d as N',
           $time,
           $rand);
         return $result['N'];
       }
     } else {
       // This is a 64 bit machine, so we can just do the math.
       return ($time << 32) + $rand;
     }
   }
 }
diff --git a/src/applications/metamta/storage/PhabricatorMetaMTAMail.php b/src/applications/metamta/storage/PhabricatorMetaMTAMail.php
index cb6bac7262..2232167845 100644
--- a/src/applications/metamta/storage/PhabricatorMetaMTAMail.php
+++ b/src/applications/metamta/storage/PhabricatorMetaMTAMail.php
@@ -1,925 +1,927 @@
 <?php
 
 /**
  * @task recipients   Managing Recipients
  */
 final class PhabricatorMetaMTAMail extends PhabricatorMetaMTADAO {
 
   const STATUS_QUEUE = 'queued';
   const STATUS_SENT  = 'sent';
   const STATUS_FAIL  = 'fail';
   const STATUS_VOID  = 'void';
 
   const RETRY_DELAY   = 5;
 
   protected $parameters;
   protected $status;
   protected $message;
   protected $relatedPHID;
 
   private $recipientExpansionMap;
 
   public function __construct() {
 
     $this->status     = self::STATUS_QUEUE;
     $this->parameters = array();
 
     parent::__construct();
   }
 
   public function getConfiguration() {
     return array(
       self::CONFIG_SERIALIZATION => array(
         'parameters'  => self::SERIALIZATION_JSON,
       ),
     ) + parent::getConfiguration();
   }
 
   protected function setParam($param, $value) {
     $this->parameters[$param] = $value;
     return $this;
   }
 
   protected function getParam($param, $default = null) {
     return idx($this->parameters, $param, $default);
   }
 
   /**
    * Set tags (@{class:MetaMTANotificationType} constants) which identify the
    * content of this mail in a general way. These tags are used to allow users
    * to opt out of receiving certain types of mail, like updates when a task's
    * projects change.
    *
    * @param list<const> List of @{class:MetaMTANotificationType} constants.
    * @return this
    */
   public function setMailTags(array $tags) {
     $this->setParam('mailtags', array_unique($tags));
     return $this;
   }
 
   public function getMailTags() {
     return $this->getParam('mailtags', array());
   }
 
   /**
    * In Gmail, conversations will be broken if you reply to a thread and the
    * server sends back a response without referencing your Message-ID, even if
    * it references a Message-ID earlier in the thread. To avoid this, use the
    * parent email's message ID explicitly if it's available. This overwrites the
    * "In-Reply-To" and "References" headers we would otherwise generate. This
    * needs to be set whenever an action is triggered by an email message. See
    * T251 for more details.
    *
    * @param   string The "Message-ID" of the email which precedes this one.
    * @return  this
    */
   public function setParentMessageID($id) {
     $this->setParam('parent-message-id', $id);
     return $this;
   }
 
   public function getParentMessageID() {
     return $this->getParam('parent-message-id');
   }
 
   public function getSubject() {
     return $this->getParam('subject');
   }
 
   public function addTos(array $phids) {
     $phids = array_unique($phids);
     $this->setParam('to', $phids);
     return $this;
   }
 
   public function addRawTos(array $raw_email) {
 
     // Strip addresses down to bare emails, since the MailAdapter API currently
     // requires we pass it just the address (like `alincoln@logcabin.org`), not
     // a full string like `"Abraham Lincoln" <alincoln@logcabin.org>`.
     foreach ($raw_email as $key => $email) {
       $object = new PhutilEmailAddress($email);
       $raw_email[$key] = $object->getAddress();
     }
 
     $this->setParam('raw-to', $raw_email);
     return $this;
   }
 
   public function addCCs(array $phids) {
     $phids = array_unique($phids);
     $this->setParam('cc', $phids);
     return $this;
   }
 
   public function setExcludeMailRecipientPHIDs(array $exclude) {
     $this->setParam('exclude', $exclude);
     return $this;
   }
 
   private function getExcludeMailRecipientPHIDs() {
     return $this->getParam('exclude', array());
   }
 
   public function getTranslation(array $objects) {
     $default_translation = PhabricatorEnv::getEnvConfig('translation.provider');
     $return = null;
     $recipients = array_merge(
       idx($this->parameters, 'to', array()),
       idx($this->parameters, 'cc', array()));
     foreach (array_select_keys($objects, $recipients) as $object) {
       $translation = null;
       if ($object instanceof PhabricatorUser) {
         $translation = $object->getTranslation();
       }
       if (!$translation) {
         $translation = $default_translation;
       }
       if ($return && $translation != $return) {
         return $default_translation;
       }
       $return = $translation;
     }
 
     if (!$return) {
       $return = $default_translation;
     }
 
     return $return;
   }
 
   public function addPHIDHeaders($name, array $phids) {
     foreach ($phids as $phid) {
       $this->addHeader($name, '<'.$phid.'>');
     }
     return $this;
   }
 
   public function addHeader($name, $value) {
     $this->parameters['headers'][] = array($name, $value);
     return $this;
   }
 
   public function addAttachment(PhabricatorMetaMTAAttachment $attachment) {
     $this->parameters['attachments'][] = $attachment->toDictionary();
     return $this;
   }
 
   public function getAttachments() {
     $dicts = $this->getParam('attachments');
 
     $result = array();
     foreach ($dicts as $dict) {
       $result[] = PhabricatorMetaMTAAttachment::newFromDictionary($dict);
     }
     return $result;
   }
 
   public function setAttachments(array $attachments) {
     assert_instances_of($attachments, 'PhabricatorMetaMTAAttachment');
     $this->setParam('attachments', mpull($attachments, 'toDictionary'));
     return $this;
   }
 
   public function setFrom($from) {
     $this->setParam('from', $from);
     return $this;
   }
 
   public function setReplyTo($reply_to) {
     $this->setParam('reply-to', $reply_to);
     return $this;
   }
 
   public function setSubject($subject) {
     $this->setParam('subject', $subject);
     return $this;
   }
 
   public function setSubjectPrefix($prefix) {
     $this->setParam('subject-prefix', $prefix);
     return $this;
   }
 
   public function setVarySubjectPrefix($prefix) {
     $this->setParam('vary-subject-prefix', $prefix);
     return $this;
   }
 
   public function setBody($body) {
     $this->setParam('body', $body);
     return $this;
   }
 
   public function getBody() {
     return $this->getParam('body');
   }
 
   public function setIsHTML($html) {
     $this->setParam('is-html', $html);
     return $this;
   }
 
   public function setIsErrorEmail($is_error) {
     $this->setParam('is-error', $is_error);
     return $this;
   }
 
   public function getIsErrorEmail() {
     return $this->getParam('is-error', false);
   }
 
   public function getToPHIDs() {
     return $this->getParam('to', array());
   }
 
   public function getRawToAddresses() {
     return $this->getParam('raw-to', array());
   }
 
   public function getCcPHIDs() {
     return $this->getParam('cc', array());
   }
 
   /**
    * Force delivery of a message, even if recipients have preferences which
    * would otherwise drop the message.
    *
    * This is primarily intended to let users who don't want any email still
    * receive things like password resets.
    *
    * @param bool  True to force delivery despite user preferences.
    * @return this
    */
   public function setForceDelivery($force) {
     $this->setParam('force', $force);
     return $this;
   }
 
   public function getForceDelivery() {
     return $this->getParam('force', false);
   }
 
   /**
    * Flag that this is an auto-generated bulk message and should have bulk
    * headers added to it if appropriate. Broadly, this means some flavor of
    * "Precedence: bulk" or similar, but is implementation and configuration
    * dependent.
    *
    * @param bool  True if the mail is automated bulk mail.
    * @return this
    */
   public function setIsBulk($is_bulk) {
     $this->setParam('is-bulk', $is_bulk);
     return $this;
   }
 
   /**
    * Use this method to set an ID used for message threading. MetaMTA will
    * set appropriate headers (Message-ID, In-Reply-To, References and
    * Thread-Index) based on the capabilities of the underlying mailer.
    *
    * @param string  Unique identifier, appropriate for use in a Message-ID,
    *                In-Reply-To or References headers.
    * @param bool    If true, indicates this is the first message in the thread.
    * @return this
    */
   public function setThreadID($thread_id, $is_first_message = false) {
     $this->setParam('thread-id', $thread_id);
     $this->setParam('is-first-message', $is_first_message);
     return $this;
   }
 
   /**
    * Save a newly created mail to the database. The mail will eventually be
    * delivered by the MetaMTA daemon.
    *
    * @return this
    */
   public function saveAndSend() {
     return $this->save();
   }
 
   public function save() {
     if ($this->getID()) {
       return parent::save();
     }
 
     // NOTE: When mail is sent from CLI scripts that run tasks in-process, we
     // may re-enter this method from within scheduleTask(). The implementation
     // is intended to avoid anything awkward if we end up reentering this
     // method.
 
     $this->openTransaction();
       // Save to generate a task ID.
       $result = parent::save();
 
       // Queue a task to send this mail.
       $mailer_task = PhabricatorWorker::scheduleTask(
         'PhabricatorMetaMTAWorker',
         $this->getID(),
         PhabricatorWorker::PRIORITY_ALERTS);
 
     $this->saveTransaction();
 
     return $result;
   }
 
   public function buildDefaultMailer() {
     return PhabricatorEnv::newObjectFromConfig('metamta.mail-adapter');
   }
 
 
   /**
    * Attempt to deliver an email immediately, in this process.
    *
    * @param bool  Try to deliver this email even if it has already been
    *              delivered or is in backoff after a failed delivery attempt.
    * @param PhabricatorMailImplementationAdapter Use a specific mail adapter,
    *              instead of the default.
    *
    * @return void
    */
   public function sendNow(
     $force_send = false,
     PhabricatorMailImplementationAdapter $mailer = null) {
 
     if ($mailer === null) {
       $mailer = $this->buildDefaultMailer();
     }
 
     if (!$force_send) {
       if ($this->getStatus() != self::STATUS_QUEUE) {
         throw new Exception('Trying to send an already-sent mail!');
       }
     }
 
     try {
       $params = $this->parameters;
 
       $actors = $this->loadAllActors();
       $deliverable_actors = $this->filterDeliverableActors($actors);
 
       $default_from = PhabricatorEnv::getEnvConfig('metamta.default-address');
       if (empty($params['from'])) {
         $mailer->setFrom($default_from);
       }
 
       $is_first = idx($params, 'is-first-message');
       unset($params['is-first-message']);
 
       $is_threaded = (bool)idx($params, 'thread-id');
 
       $reply_to_name = idx($params, 'reply-to-name', '');
       unset($params['reply-to-name']);
 
       $add_cc = array();
       $add_to = array();
 
       foreach ($params as $key => $value) {
         switch ($key) {
           case 'from':
             $from = $value;
             $actor_email = null;
             $actor_name = null;
             $actor = idx($actors, $from);
             if ($actor) {
               $actor_email = $actor->getEmailAddress();
               $actor_name = $actor->getName();
             }
             $can_send_as_user = $actor_email &&
               PhabricatorEnv::getEnvConfig('metamta.can-send-as-user');
 
             if ($can_send_as_user) {
               $mailer->setFrom($actor_email, $actor_name);
             } else {
               $from_email = coalesce($actor_email, $default_from);
               $from_name = coalesce($actor_name, pht('Phabricator'));
 
               if (empty($params['reply-to'])) {
                 $params['reply-to'] = $from_email;
                 $params['reply-to-name'] = $from_name;
               }
 
               $mailer->setFrom($default_from, $from_name);
             }
             break;
           case 'reply-to':
             $mailer->addReplyTo($value, $reply_to_name);
             break;
           case 'to':
             $to_phids = $this->expandRecipients($value);
             $to_actors = array_select_keys($deliverable_actors, $to_phids);
             $add_to = array_merge(
               $add_to,
               mpull($to_actors, 'getEmailAddress'));
             break;
           case 'raw-to':
             $add_to = array_merge($add_to, $value);
             break;
           case 'cc':
             $cc_phids = $this->expandRecipients($value);
             $cc_actors = array_select_keys($deliverable_actors, $cc_phids);
             $add_cc = array_merge(
               $add_cc,
               mpull($cc_actors, 'getEmailAddress'));
             break;
           case 'headers':
             foreach ($value as $pair) {
               list($header_key, $header_value) = $pair;
 
               // NOTE: If we have \n in a header, SES rejects the email.
               $header_value = str_replace("\n", ' ', $header_value);
 
               $mailer->addHeader($header_key, $header_value);
             }
             break;
           case 'attachments':
             $value = $this->getAttachments();
             foreach ($value as $attachment) {
               $mailer->addAttachment(
                 $attachment->getData(),
                 $attachment->getFilename(),
                 $attachment->getMimeType());
             }
             break;
           case 'body':
             $max = PhabricatorEnv::getEnvConfig('metamta.email-body-limit');
             if (strlen($value) > $max) {
               $value = phutil_utf8_shorten($value, $max);
               $value .= "\n";
               $value .= pht('(This email was truncated at %d bytes.)', $max);
             }
             $mailer->setBody($value);
             break;
           case 'subject':
             // Only try to use preferences if everything is multiplexed, so we
             // get consistent behavior.
             $use_prefs = self::shouldMultiplexAllMail();
 
             $prefs = null;
             if ($use_prefs) {
 
               // If multiplexing is enabled, some recipients will be in "Cc"
               // rather than "To". We'll move them to "To" later (or supply a
               // dummy "To") but need to look for the recipient in either the
               // "To" or "Cc" fields here.
               $target_phid = head(idx($params, 'to', array()));
               if (!$target_phid) {
                 $target_phid = head(idx($params, 'cc', array()));
               }
 
               if ($target_phid) {
                 $user = id(new PhabricatorUser())->loadOneWhere(
                   'phid = %s',
                   $target_phid);
                 if ($user) {
                   $prefs = $user->loadPreferences();
                 }
               }
             }
 
             $subject = array();
 
             if ($is_threaded) {
               $add_re = PhabricatorEnv::getEnvConfig('metamta.re-prefix');
 
               if ($prefs) {
                 $add_re = $prefs->getPreference(
                   PhabricatorUserPreferences::PREFERENCE_RE_PREFIX,
                   $add_re);
               }
 
               if ($add_re) {
                 $subject[] = 'Re:';
               }
             }
 
             $subject[] = trim(idx($params, 'subject-prefix'));
 
             $vary_prefix = idx($params, 'vary-subject-prefix');
             if ($vary_prefix != '') {
               $use_subject = PhabricatorEnv::getEnvConfig(
                 'metamta.vary-subjects');
 
               if ($prefs) {
                 $use_subject = $prefs->getPreference(
                   PhabricatorUserPreferences::PREFERENCE_VARY_SUBJECT,
                   $use_subject);
               }
 
               if ($use_subject) {
                 $subject[] = $vary_prefix;
               }
             }
 
             $subject[] = $value;
 
             $mailer->setSubject(implode(' ', array_filter($subject)));
             break;
           case 'is-html':
             if ($value) {
               $mailer->setIsHTML(true);
             }
             break;
           case 'is-bulk':
             if ($value) {
               if (PhabricatorEnv::getEnvConfig('metamta.precedence-bulk')) {
                 $mailer->addHeader('Precedence', 'bulk');
               }
             }
             break;
           case 'thread-id':
 
             // NOTE: Gmail freaks out about In-Reply-To and References which
             // aren't in the form "<string@domain.tld>"; this is also required
             // by RFC 2822, although some clients are more liberal in what they
             // accept.
             $domain = PhabricatorEnv::getEnvConfig('metamta.domain');
             $value = '<'.$value.'@'.$domain.'>';
 
             if ($is_first && $mailer->supportsMessageIDHeader()) {
               $mailer->addHeader('Message-ID',  $value);
             } else {
               $in_reply_to = $value;
               $references = array($value);
               $parent_id = $this->getParentMessageID();
               if ($parent_id) {
                 $in_reply_to = $parent_id;
                 // By RFC 2822, the most immediate parent should appear last
                 // in the "References" header, so this order is intentional.
                 $references[] = $parent_id;
               }
               $references = implode(' ', $references);
               $mailer->addHeader('In-Reply-To', $in_reply_to);
               $mailer->addHeader('References',  $references);
             }
             $thread_index = $this->generateThreadIndex($value, $is_first);
             $mailer->addHeader('Thread-Index', $thread_index);
             break;
           case 'mailtags':
             // Handled below.
             break;
           case 'subject-prefix':
           case 'vary-subject-prefix':
             // Handled above.
             break;
           default:
             // Just discard.
         }
       }
 
       if (!$add_to && !$add_cc) {
         $this->setStatus(self::STATUS_VOID);
         $this->setMessage(
           'Message has no valid recipients: all To/Cc are disabled, invalid, '.
           'or configured not to receive this mail.');
         return $this->save();
       }
 
       if ($this->getIsErrorEmail()) {
         $all_recipients = array_merge($add_to, $add_cc);
         if ($this->shouldRateLimitMail($all_recipients)) {
           $this->setStatus(self::STATUS_VOID);
           $this->setMessage(
             pht(
               'This is an error email, but one or more recipients have '.
               'exceeded the error email rate limit. Declining to deliver '.
               'message.'));
           return $this->save();
         }
       }
 
       $mailer->addHeader('X-Phabricator-Sent-This-Message', 'Yes');
       $mailer->addHeader('X-Mail-Transport-Agent', 'MetaMTA');
 
       // Some clients respect this to suppress OOF and other auto-responses.
       $mailer->addHeader('X-Auto-Response-Suppress', 'All');
 
       // If the message has mailtags, filter out any recipients who don't want
       // to receive this type of mail.
       $mailtags = $this->getParam('mailtags');
       if ($mailtags) {
         $tag_header = array();
         foreach ($mailtags as $mailtag) {
           $tag_header[] = '<'.$mailtag.'>';
         }
         $tag_header = implode(', ', $tag_header);
         $mailer->addHeader('X-Phabricator-Mail-Tags', $tag_header);
       }
 
       // Some mailers require a valid "To:" in order to deliver mail. If we
       // don't have any "To:", try to fill it in with a placeholder "To:".
       // If that also fails, move the "Cc:" line to "To:".
       if (!$add_to) {
         $placeholder_key = 'metamta.placeholder-to-recipient';
         $placeholder = PhabricatorEnv::getEnvConfig($placeholder_key);
         if ($placeholder !== null) {
           $add_to = array($placeholder);
         } else {
           $add_to = $add_cc;
           $add_cc = array();
         }
       }
 
       $add_to = array_unique($add_to);
       $add_cc = array_diff(array_unique($add_cc), $add_to);
 
       $mailer->addTos($add_to);
       if ($add_cc) {
         $mailer->addCCs($add_cc);
       }
     } catch (Exception $ex) {
       $this
         ->setStatus(self::STATUS_FAIL)
         ->setMessage($ex->getMessage())
         ->save();
 
       throw $ex;
     }
 
     try {
       $ok = $mailer->send();
       if (!$ok) {
         // TODO: At some point, we should clean this up and make all mailers
         // throw.
         throw new Exception(
           pht('Mail adapter encountered an unexpected, unspecified failure.'));
       }
 
       $this->setStatus(self::STATUS_SENT);
       $this->save();
 
       return $this;
     } catch (PhabricatorMetaMTAPermanentFailureException $ex) {
       $this
         ->setStatus(self::STATUS_FAIL)
         ->setMessage($ex->getMessage())
         ->save();
 
       throw $ex;
     } catch (Exception $ex) {
       $this
         ->setMessage($ex->getMessage()."\n".$ex->getTraceAsString())
         ->save();
 
       throw $ex;
     }
   }
 
   public static function getReadableStatus($status_code) {
     static $readable = array(
       self::STATUS_QUEUE => 'Queued for Delivery',
       self::STATUS_FAIL  => 'Delivery Failed',
       self::STATUS_SENT  => 'Sent',
       self::STATUS_VOID  => 'Void',
     );
     $status_code = coalesce($status_code, '?');
     return idx($readable, $status_code, $status_code);
   }
 
   private function generateThreadIndex($seed, $is_first_mail) {
     // When threading, Outlook ignores the 'References' and 'In-Reply-To'
     // headers that most clients use. Instead, it uses a custom 'Thread-Index'
     // header. The format of this header is something like this (from
     // camel-exchange-folder.c in Evolution Exchange):
 
     /* A new post to a folder gets a 27-byte-long thread index. (The value
      * is apparently unique but meaningless.) Each reply to a post gets a
      * 32-byte-long thread index whose first 27 bytes are the same as the
      * parent's thread index. Each reply to any of those gets a
      * 37-byte-long thread index, etc. The Thread-Index header contains a
      * base64 representation of this value.
      */
 
     // The specific implementation uses a 27-byte header for the first email
     // a recipient receives, and a random 5-byte suffix (32 bytes total)
     // thereafter. This means that all the replies are (incorrectly) siblings,
     // but it would be very difficult to keep track of the entire tree and this
     // gets us reasonable client behavior.
 
     $base = substr(md5($seed), 0, 27);
     if (!$is_first_mail) {
       // Not totally sure, but it seems like outlook orders replies by
       // thread-index rather than timestamp, so to get these to show up in the
       // right order we use the time as the last 4 bytes.
       $base .= ' '.pack('N', time());
     }
 
     return base64_encode($base);
   }
 
   public static function shouldMultiplexAllMail() {
     return PhabricatorEnv::getEnvConfig('metamta.one-mail-per-recipient');
   }
 
 
 /* -(  Managing Recipients  )------------------------------------------------ */
 
 
   /**
    * Get all of the recipients for this mail, after preference filters are
    * applied. This list has all objects to whom delivery will be attempted.
    *
    * @return  list<phid>  A list of all recipients to whom delivery will be
    *                      attempted.
    * @task recipients
    */
   public function buildRecipientList() {
     $actors = $this->loadActors(
       array_merge(
         $this->getToPHIDs(),
         $this->getCcPHIDs()));
     $actors = $this->filterDeliverableActors($actors);
     return mpull($actors, 'getPHID');
   }
 
   public function loadAllActors() {
     $actor_phids = array_merge(
       array($this->getParam('from')),
       $this->getToPHIDs(),
       $this->getCcPHIDs());
 
     $this->loadRecipientExpansions($actor_phids);
     $actor_phids = $this->expandRecipients($actor_phids);
 
     return $this->loadActors($actor_phids);
   }
 
   private function loadRecipientExpansions(array $phids) {
     $expansions = id(new PhabricatorMetaMTAMemberQuery())
       ->setViewer(PhabricatorUser::getOmnipotentUser())
       ->withPHIDs($phids)
       ->execute();
 
     $this->recipientExpansionMap = $expansions;
 
     return $this;
   }
 
   /**
    * Expand a list of recipient PHIDs (possibly including aggregate recipients
    * like projects) into a deaggregated list of individual recipient PHIDs.
    * For example, this will expand project PHIDs into a list of the project's
    * members.
    *
    * @param list<phid>  List of recipient PHIDs, possibly including aggregate
    *                    recipients.
    * @return list<phid> Deaggregated list of mailable recipients.
    */
   private function expandRecipients(array $phids) {
     if ($this->recipientExpansionMap === null) {
       throw new Exception(
         pht(
           'Call loadRecipientExpansions() before expandRecipients()!'));
     }
 
     $results = array();
     foreach ($phids as $phid) {
       if (!isset($this->recipientExpansionMap[$phid])) {
         $results[$phid] = $phid;
       } else {
         foreach ($this->recipientExpansionMap[$phid] as $recipient_phid) {
           $results[$recipient_phid] = $recipient_phid;
         }
       }
     }
 
     return array_keys($results);
   }
 
   private function filterDeliverableActors(array $actors) {
     assert_instances_of($actors, 'PhabricatorMetaMTAActor');
     $deliverable_actors = array();
     foreach ($actors as $phid => $actor) {
       if ($actor->isDeliverable()) {
         $deliverable_actors[$phid] = $actor;
       }
     }
     return $deliverable_actors;
   }
 
   private function loadActors(array $actor_phids) {
     $actor_phids = array_filter($actor_phids);
     $viewer = PhabricatorUser::getOmnipotentUser();
 
     $actors = id(new PhabricatorMetaMTAActorQuery())
       ->setViewer($viewer)
       ->withPHIDs($actor_phids)
       ->execute();
 
     if (!$actors) {
       return array();
     }
 
     if ($this->getForceDelivery()) {
       // If we're forcing delivery, skip all the opt-out checks.
       return $actors;
     }
 
     // Exclude explicit recipients.
     foreach ($this->getExcludeMailRecipientPHIDs() as $phid) {
       $actor = idx($actors, $phid);
       if (!$actor) {
         continue;
       }
       $actor->setUndeliverable(
         pht(
           'This message is a response to another email message, and this '.
           'recipient received the original email message, so we are not '.
           'sending them this substantially similar message (for example, '.
           'the sender used "Reply All" instead of "Reply" in response to '.
           'mail from Phabricator).'));
     }
 
     // Exclude the actor if their preferences are set.
     $from_phid = $this->getParam('from');
     $from_actor = idx($actors, $from_phid);
     if ($from_actor) {
       $from_user = id(new PhabricatorPeopleQuery())
         ->setViewer($viewer)
         ->withPHIDs(array($from_phid))
         ->execute();
       $from_user = head($from_user);
       if ($from_user) {
         $pref_key = PhabricatorUserPreferences::PREFERENCE_NO_SELF_MAIL;
         $exclude_self = $from_user
           ->loadPreferences()
           ->getPreference($pref_key);
         if ($exclude_self) {
           $from_actor->setUndeliverable(
             pht(
               'This recipient is the user whose actions caused delivery of '.
               'this message, but they have set preferences so they do not '.
               'receive mail about their own actions (Settings > Email '.
               'Preferences > Self Actions).'));
         }
       }
     }
 
     $all_prefs = id(new PhabricatorUserPreferences())->loadAllWhere(
       'userPHID in (%Ls)',
       $actor_phids);
     $all_prefs = mpull($all_prefs, null, 'getUserPHID');
 
     // Exclude recipients who don't want any mail.
     foreach ($all_prefs as $phid => $prefs) {
       $exclude = $prefs->getPreference(
         PhabricatorUserPreferences::PREFERENCE_NO_MAIL,
         false);
       if ($exclude) {
         $actors[$phid]->setUndeliverable(
           pht(
             'This recipient has disabled all email notifications '.
             '(Settings > Email Preferences > Email Notifications).'));
       }
     }
 
+    $value_email = PhabricatorUserPreferences::MAILTAG_PREFERENCE_EMAIL;
+
     // Exclude all recipients who have set preferences to not receive this type
     // of email (for example, a user who says they don't want emails about task
     // CC changes).
     $tags = $this->getParam('mailtags');
     if ($tags) {
       foreach ($all_prefs as $phid => $prefs) {
         $user_mailtags = $prefs->getPreference(
           PhabricatorUserPreferences::PREFERENCE_MAILTAGS,
           array());
 
         // The user must have elected to receive mail for at least one
         // of the mailtags.
         $send = false;
         foreach ($tags as $tag) {
-          if (idx($user_mailtags, $tag, true)) {
+          if (((int)idx($user_mailtags, $tag, $value_email)) == $value_email) {
             $send = true;
             break;
           }
         }
 
         if (!$send) {
           $actors[$phid]->setUndeliverable(
             pht(
               'This mail has tags which control which users receive it, and '.
               'this recipient has not elected to receive mail with any of '.
               'the tags on this message (Settings > Email Preferences).'));
         }
       }
     }
 
     return $actors;
   }
 
   private function shouldRateLimitMail(array $all_recipients) {
     try {
       PhabricatorSystemActionEngine::willTakeAction(
         $all_recipients,
         new PhabricatorMetaMTAErrorMailAction(),
         1);
       return false;
     } catch (PhabricatorSystemActionRateLimitException $ex) {
       return true;
     }
   }
 
 
 }
diff --git a/src/applications/settings/panel/PhabricatorSettingsPanelEmailPreferences.php b/src/applications/settings/panel/PhabricatorSettingsPanelEmailPreferences.php
index 9a966cbca9..68bb52c24d 100644
--- a/src/applications/settings/panel/PhabricatorSettingsPanelEmailPreferences.php
+++ b/src/applications/settings/panel/PhabricatorSettingsPanelEmailPreferences.php
@@ -1,232 +1,255 @@
 <?php
 
 final class PhabricatorSettingsPanelEmailPreferences
   extends PhabricatorSettingsPanel {
 
   public function getPanelKey() {
     return 'emailpreferences';
   }
 
   public function getPanelName() {
     return pht('Email Preferences');
   }
 
   public function getPanelGroup() {
     return pht('Email');
   }
 
   public function processRequest(AphrontRequest $request) {
     $user = $request->getUser();
 
     $preferences = $user->loadPreferences();
 
     $pref_no_mail = PhabricatorUserPreferences::PREFERENCE_NO_MAIL;
     $pref_no_self_mail = PhabricatorUserPreferences::PREFERENCE_NO_SELF_MAIL;
 
+    $value_email = PhabricatorUserPreferences::MAILTAG_PREFERENCE_EMAIL;
+
     $errors = array();
     if ($request->isFormPost()) {
       $preferences->setPreference(
         $pref_no_mail,
         $request->getStr($pref_no_mail));
 
       $preferences->setPreference(
         $pref_no_self_mail,
         $request->getStr($pref_no_self_mail));
 
       $new_tags = $request->getArr('mailtags');
       $mailtags = $preferences->getPreference('mailtags', array());
       $all_tags = $this->getAllTags($user);
 
       foreach ($all_tags as $key => $label) {
-        $mailtags[$key] = (bool)idx($new_tags, $key, false);
+        $mailtags[$key] = (int)idx($new_tags, $key, $value_email);
       }
       $preferences->setPreference('mailtags', $mailtags);
 
       $preferences->save();
 
       return id(new AphrontRedirectResponse())
         ->setURI($this->getPanelURI('?saved=true'));
     }
 
     $form = new AphrontFormView();
     $form
       ->setUser($user)
       ->appendRemarkupInstructions(
         pht(
           'These settings let you control how Phabricator notifies you about '.
           'events. You can configure Phabricator to send you an email, '.
           'just send a web notification, or not notify you at all.'))
       ->appendRemarkupInstructions(
         pht(
           'If you disable **Email Notifications**, Phabricator will never '.
           'send email to notify you about events. This preference overrides '.
           'all your other settings.'.
           "\n\n".
           "//You may still receive some administrative email, like password ".
           "reset email.//"))
       ->appendChild(
         id(new AphrontFormSelectControl())
           ->setLabel(pht('Email Notifications'))
           ->setName($pref_no_mail)
           ->setOptions(
             array(
               '0' => pht('Send me email notifications'),
               '1' => pht('Never send email notifications'),
             ))
           ->setValue($preferences->getPreference($pref_no_mail, 0)))
       ->appendRemarkupInstructions(
         pht(
           'If you disable **Self Actions**, Phabricator will not notify '.
           'you about actions you take.'))
       ->appendChild(
         id(new AphrontFormSelectControl())
           ->setLabel(pht('Self Actions'))
           ->setName($pref_no_self_mail)
           ->setOptions(
             array(
               '0' => pht('Send me an email when I take an action'),
               '1' => pht('Do not send me an email when I take an action'),
             ))
           ->setValue($preferences->getPreference($pref_no_self_mail, 0)));
 
     $mailtags = $preferences->getPreference('mailtags', array());
 
     $form->appendChild(
       id(new PHUIFormDividerControl()));
 
     $form->appendRemarkupInstructions(
       pht(
-        'You can customize which kinds of events you receive email for '.
-        'here. If you turn off email for a certain type of event, you '.
-        'will receive an unread notification in Phabricator instead.'.
+        'You can adjust **Application Settings** here to customize when '.
+        'you are emailed and notified.'.
         "\n\n".
-        'Phabricator notifications (shown in the menu bar) which you receive '.
-        'an email for are marked read by default in Phabricator. If you turn '.
-        'off email for a certain type of event, the corresponding '.
-        'notification will not be marked read.'.
+        "| Setting | Effect\n".
+        "| ------- | -------\n".
+        "| Email | You will receive an email and a notification, but the ".
+        "notification will be marked \"read\".\n".
+        "| Notify | You will receive an unread notification only.\n".
+        "| Ignore | You will receive nothing.\n".
         "\n\n".
-        'Note that if an update makes several changes (like adding CCs to a '.
-        'task, closing it, and adding a comment) you will still receive '.
-        'an email as long as at least one of the changes is set to notify '.
-        'you.'.
+        'If an update makes several changes (like adding CCs to a task, '.
+        'closing it, and adding a comment) you will receive the strongest '.
+        'notification any of the changes is configured to deliver.'.
         "\n\n".
         'These preferences **only** apply to objects you are connected to '.
         '(for example, Revisions where you are a reviewer or tasks you are '.
         'CC\'d on). To receive email alerts when other objects are created, '.
-        'configure [[ /herald/ | Herald Rules ]].'.
-        "\n\n".
-        'Phabricator will send an email to your primary account when:'));
+        'configure [[ /herald/ | Herald Rules ]].'));
 
     $editors = $this->getAllEditorsWithTags($user);
 
     // Find all the tags shared by more than one application, and put them
     // in a "common" group.
     $all_tags = array();
     foreach ($editors as $editor) {
       foreach ($editor->getMailTagsMap() as $tag => $name) {
         if (empty($all_tags[$tag])) {
           $all_tags[$tag] = array(
             'count' => 0,
             'name' => $name,
           );
         }
         $all_tags[$tag]['count'];
       }
     }
 
     $common_tags = array();
     foreach ($all_tags as $tag => $info) {
       if ($info['count'] > 1) {
         $common_tags[$tag] = $info['name'];
       }
     }
 
     // Build up the groups of application-specific options.
     $tag_groups = array();
     foreach ($editors as $editor) {
       $tag_groups[] = array(
         $editor->getEditorObjectsDescription(),
         array_diff_key($editor->getMailTagsMap(), $common_tags));
     }
 
     // Sort them, then put "Common" at the top.
     $tag_groups = isort($tag_groups, 0);
     if ($common_tags) {
       array_unshift($tag_groups, array(pht('Common'), $common_tags));
     }
 
     // Finally, build the controls.
     foreach ($tag_groups as $spec) {
       list($label, $map) = $spec;
       $control = $this->buildMailTagControl($label, $map, $mailtags);
       $form->appendChild($control);
     }
 
     $form
       ->appendChild(
         id(new AphrontFormSubmitControl())
           ->setValue(pht('Save Preferences')));
 
     $form_box = id(new PHUIObjectBoxView())
       ->setHeaderText(pht('Email Preferences'))
       ->setFormSaved($request->getStr('saved'))
       ->setFormErrors($errors)
       ->setForm($form);
 
     return id(new AphrontNullView())
       ->appendChild(
         array(
           $form_box,
         ));
   }
 
   private function getAllEditorsWithTags(PhabricatorUser $user) {
     $editors = id(new PhutilSymbolLoader())
       ->setAncestorClass('PhabricatorApplicationTransactionEditor')
       ->loadObjects();
 
     foreach ($editors as $key => $editor) {
       // Remove editors which do not support mail tags.
       if (!$editor->getMailTagsMap()) {
         unset($editors[$key]);
       }
 
       // Remove editors for applications which are not installed.
       $app = $editor->getEditorApplicationClass();
       if ($app !== null) {
         if (!PhabricatorApplication::isClassInstalledForViewer($app, $user)) {
           unset($editors[$key]);
         }
       }
     }
 
     return $editors;
   }
 
   private function getAllTags(PhabricatorUser $user) {
     $tags = array();
     foreach ($this->getAllEditorsWithTags($user) as $editor) {
       $tags += $editor->getMailTagsMap();
     }
     return $tags;
   }
 
   private function buildMailTagControl(
     $control_label,
     array $tags,
     array $prefs) {
 
-    $control = new AphrontFormCheckboxControl();
-    $control->setLabel($control_label);
+    $value_email = PhabricatorUserPreferences::MAILTAG_PREFERENCE_EMAIL;
+    $value_notify = PhabricatorUserPreferences::MAILTAG_PREFERENCE_NOTIFY;
+    $value_ignore = PhabricatorUserPreferences::MAILTAG_PREFERENCE_IGNORE;
+
+    $content = array();
     foreach ($tags as $key => $label) {
-      $control->addCheckbox(
-        'mailtags['.$key.']',
-        1,
-        $label,
-        idx($prefs, $key, 1));
+      $select = AphrontFormSelectControl::renderSelectTag(
+        (int)idx($prefs, $key, $value_email),
+        array(
+          $value_email => pht("\xE2\x9A\xAB Email"),
+          $value_notify => pht("\xE2\x97\x90 Notify"),
+          $value_ignore => pht("\xE2\x9A\xAA Ignore"),
+        ),
+        array(
+          'name' => 'mailtags['.$key.']',
+        ));
+
+      $content[] = phutil_tag(
+        'div',
+        array(
+          'class' => 'psb',
+        ),
+        array(
+          $select,
+          ' ',
+          $label,
+        ));
     }
 
+    $control = new AphrontFormStaticControl();
+    $control->setLabel($control_label);
+    $control->setValue($content);
+
     return $control;
   }
 
 }
diff --git a/src/applications/settings/storage/PhabricatorUserPreferences.php b/src/applications/settings/storage/PhabricatorUserPreferences.php
index f4e931bf6a..f882bddd9a 100644
--- a/src/applications/settings/storage/PhabricatorUserPreferences.php
+++ b/src/applications/settings/storage/PhabricatorUserPreferences.php
@@ -1,90 +1,95 @@
 <?php
 
 final class PhabricatorUserPreferences extends PhabricatorUserDAO {
 
   const PREFERENCE_MONOSPACED           = 'monospaced';
   const PREFERENCE_DARK_CONSOLE         = 'dark_console';
   const PREFERENCE_EDITOR               = 'editor';
   const PREFERENCE_MULTIEDIT            = 'multiedit';
   const PREFERENCE_TITLES               = 'titles';
   const PREFERENCE_MONOSPACED_TEXTAREAS = 'monospaced-textareas';
   const PREFERENCE_TIME_FORMAT          = 'time-format';
 
   const PREFERENCE_RE_PREFIX            = 're-prefix';
   const PREFERENCE_NO_SELF_MAIL         = 'self-mail';
   const PREFERENCE_NO_MAIL              = 'no-mail';
   const PREFERENCE_MAILTAGS             = 'mailtags';
   const PREFERENCE_VARY_SUBJECT         = 'vary-subject';
 
   const PREFERENCE_SEARCHBAR_JUMP       = 'searchbar-jump';
   const PREFERENCE_SEARCH_SHORTCUT      = 'search-shortcut';
 
   const PREFERENCE_DIFFUSION_BLAME      = 'diffusion-blame';
   const PREFERENCE_DIFFUSION_COLOR      = 'diffusion-color';
 
   const PREFERENCE_NAV_COLLAPSED        = 'nav-collapsed';
   const PREFERENCE_NAV_WIDTH            = 'nav-width';
   const PREFERENCE_APP_TILES            = 'app-tiles';
   const PREFERENCE_APP_PINNED           = 'app-pinned';
 
   const PREFERENCE_DIFF_FILETREE        = 'diff-filetree';
 
   const PREFERENCE_CONPH_NOTIFICATIONS  = 'conph-notifications';
 
+  // These are in an unusual order for historic reasons.
+  const MAILTAG_PREFERENCE_NOTIFY       = 0;
+  const MAILTAG_PREFERENCE_EMAIL        = 1;
+  const MAILTAG_PREFERENCE_IGNORE       = 2;
+
   protected $userPHID;
   protected $preferences = array();
 
   public function getConfiguration() {
     return array(
       self::CONFIG_SERIALIZATION => array(
         'preferences' => self::SERIALIZATION_JSON,
       ),
       self::CONFIG_TIMESTAMPS => false,
     ) + parent::getConfiguration();
   }
 
   public function getPreference($key, $default = null) {
     return idx($this->preferences, $key, $default);
   }
 
   public function setPreference($key, $value) {
     $this->preferences[$key] = $value;
     return $this;
   }
 
   public function unsetPreference($key) {
     unset($this->preferences[$key]);
     return $this;
   }
 
   public function getPinnedApplications(array $apps, PhabricatorUser $viewer) {
     $pref_pinned = PhabricatorUserPreferences::PREFERENCE_APP_PINNED;
     $pinned = $this->getPreference($pref_pinned);
 
     if ($pinned) {
       return $pinned;
     }
 
     $pref_tiles = PhabricatorUserPreferences::PREFERENCE_APP_TILES;
     $tiles = $this->getPreference($pref_tiles, array());
     $full_tile = 'full';
 
     $large = array();
     foreach ($apps as $app) {
       $show = $app->isPinnedByDefault($viewer);
 
       // TODO: This is legacy stuff, clean it up eventually. This approximately
       // retains the old "tiles" preference.
       if (isset($tiles[get_class($app)])) {
         $show = ($tiles[get_class($app)] == $full_tile);
       }
 
       if ($show) {
         $large[] = get_class($app);
       }
     }
 
     return $large;
   }
 
 }
diff --git a/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php b/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php
index 99544f9d73..72d59d40c5 100644
--- a/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php
+++ b/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php
@@ -1,2454 +1,2455 @@
 <?php
 
 /**
  * @task mail   Sending Mail
  * @task feed   Publishing Feed Stories
  * @task search Search Index
  * @task files  Integration with Files
  */
 abstract class PhabricatorApplicationTransactionEditor
   extends PhabricatorEditor {
 
   private $contentSource;
   private $object;
   private $xactions;
 
   private $isNewObject;
   private $mentionedPHIDs;
   private $continueOnNoEffect;
   private $continueOnMissingFields;
   private $parentMessageID;
   private $heraldAdapter;
   private $heraldTranscript;
   private $subscribers;
 
   private $isPreview;
   private $isHeraldEditor;
   private $isInverseEdgeEditor;
   private $actingAsPHID;
   private $disableEmail;
 
 
   /**
    * Get the class name for the application this editor is a part of.
    *
    * Uninstalling the application will disable the editor.
    *
    * @return string Editor's application class name.
    */
   abstract public function getEditorApplicationClass();
 
 
   /**
    * Get a description of the objects this editor edits, like "Differential
    * Revisions".
    *
    * @return string Human readable description of edited objects.
    */
   abstract public function getEditorObjectsDescription();
 
 
   public function setActingAsPHID($acting_as_phid) {
     $this->actingAsPHID = $acting_as_phid;
     return $this;
   }
 
   public function getActingAsPHID() {
     if ($this->actingAsPHID) {
       return $this->actingAsPHID;
     }
     return $this->getActor()->getPHID();
   }
 
 
   /**
    * When the editor tries to apply transactions that have no effect, should
    * it raise an exception (default) or drop them and continue?
    *
    * Generally, you will set this flag for edits coming from "Edit" interfaces,
    * and leave it cleared for edits coming from "Comment" interfaces, so the
    * user will get a useful error if they try to submit a comment that does
    * nothing (e.g., empty comment with a status change that has already been
    * performed by another user).
    *
    * @param bool  True to drop transactions without effect and continue.
    * @return this
    */
   public function setContinueOnNoEffect($continue) {
     $this->continueOnNoEffect = $continue;
     return $this;
   }
 
   public function getContinueOnNoEffect() {
     return $this->continueOnNoEffect;
   }
 
 
   /**
    * When the editor tries to apply transactions which don't populate all of
    * an object's required fields, should it raise an exception (default) or
    * drop them and continue?
    *
    * For example, if a user adds a new required custom field (like "Severity")
    * to a task, all existing tasks won't have it populated. When users
    * manually edit existing tasks, it's usually desirable to have them provide
    * a severity. However, other operations (like batch editing just the
    * owner of a task) will fail by default.
    *
    * By setting this flag for edit operations which apply to specific fields
    * (like the priority, batch, and merge editors in Maniphest), these
    * operations can continue to function even if an object is outdated.
    *
    * @param bool  True to continue when transactions don't completely satisfy
    *              all required fields.
    * @return this
    */
   public function setContinueOnMissingFields($continue_on_missing_fields) {
     $this->continueOnMissingFields = $continue_on_missing_fields;
     return $this;
   }
 
   public function getContinueOnMissingFields() {
     return $this->continueOnMissingFields;
   }
 
 
   /**
    * Not strictly necessary, but reply handlers ideally set this value to
    * make email threading work better.
    */
   public function setParentMessageID($parent_message_id) {
     $this->parentMessageID = $parent_message_id;
     return $this;
   }
   public function getParentMessageID() {
     return $this->parentMessageID;
   }
 
   public function getIsNewObject() {
     return $this->isNewObject;
   }
 
   protected function getMentionedPHIDs() {
     return $this->mentionedPHIDs;
   }
 
   public function setIsPreview($is_preview) {
     $this->isPreview = $is_preview;
     return $this;
   }
 
   public function getIsPreview() {
     return $this->isPreview;
   }
 
   public function setIsInverseEdgeEditor($is_inverse_edge_editor) {
     $this->isInverseEdgeEditor = $is_inverse_edge_editor;
     return $this;
   }
 
   public function getIsInverseEdgeEditor() {
     return $this->isInverseEdgeEditor;
   }
 
   public function setIsHeraldEditor($is_herald_editor) {
     $this->isHeraldEditor = $is_herald_editor;
     return $this;
   }
 
   public function getIsHeraldEditor() {
     return $this->isHeraldEditor;
   }
 
   /**
    * Prevent this editor from generating email when applying transactions.
    *
    * @param bool  True to disable email.
    * @return this
    */
   public function setDisableEmail($disable_email) {
     $this->disableEmail = $disable_email;
     return $this;
   }
 
   public function getDisableEmail() {
     return $this->disableEmail;
   }
 
   public function getTransactionTypes() {
     $types = array();
 
     if ($this->object instanceof PhabricatorSubscribableInterface) {
       $types[] = PhabricatorTransactions::TYPE_SUBSCRIBERS;
     }
 
     if ($this->object instanceof PhabricatorCustomFieldInterface) {
       $types[] = PhabricatorTransactions::TYPE_CUSTOMFIELD;
     }
 
     if ($this->object instanceof HarbormasterBuildableInterface) {
       $types[] = PhabricatorTransactions::TYPE_BUILDABLE;
     }
 
     if ($this->object instanceof PhabricatorTokenReceiverInterface) {
       $types[] = PhabricatorTransactions::TYPE_TOKEN;
     }
 
     if ($this->object instanceof PhabricatorProjectInterface) {
       $types[] = PhabricatorTransactions::TYPE_EDGE;
     }
 
     return $types;
   }
 
   private function adjustTransactionValues(
     PhabricatorLiskDAO $object,
     PhabricatorApplicationTransaction $xaction) {
 
     if ($xaction->shouldGenerateOldValue()) {
       $old = $this->getTransactionOldValue($object, $xaction);
       $xaction->setOldValue($old);
     }
 
     $new = $this->getTransactionNewValue($object, $xaction);
     $xaction->setNewValue($new);
   }
 
   private function getTransactionOldValue(
     PhabricatorLiskDAO $object,
     PhabricatorApplicationTransaction $xaction) {
     switch ($xaction->getTransactionType()) {
       case PhabricatorTransactions::TYPE_SUBSCRIBERS:
         return array_values($this->subscribers);
       case PhabricatorTransactions::TYPE_VIEW_POLICY:
         return $object->getViewPolicy();
       case PhabricatorTransactions::TYPE_EDIT_POLICY:
         return $object->getEditPolicy();
       case PhabricatorTransactions::TYPE_JOIN_POLICY:
         return $object->getJoinPolicy();
       case PhabricatorTransactions::TYPE_EDGE:
         $edge_type = $xaction->getMetadataValue('edge:type');
         if (!$edge_type) {
           throw new Exception("Edge transaction has no 'edge:type'!");
         }
 
         $old_edges = array();
         if ($object->getPHID()) {
           $edge_src = $object->getPHID();
 
           $old_edges = id(new PhabricatorEdgeQuery())
             ->withSourcePHIDs(array($edge_src))
             ->withEdgeTypes(array($edge_type))
             ->needEdgeData(true)
             ->execute();
 
           $old_edges = $old_edges[$edge_src][$edge_type];
         }
         return $old_edges;
       case PhabricatorTransactions::TYPE_CUSTOMFIELD:
         // NOTE: Custom fields have their old value pre-populated when they are
         // built by PhabricatorCustomFieldList.
         return $xaction->getOldValue();
       case PhabricatorTransactions::TYPE_COMMENT:
         return null;
       default:
         return $this->getCustomTransactionOldValue($object, $xaction);
     }
   }
 
   private function getTransactionNewValue(
     PhabricatorLiskDAO $object,
     PhabricatorApplicationTransaction $xaction) {
     switch ($xaction->getTransactionType()) {
       case PhabricatorTransactions::TYPE_SUBSCRIBERS:
         return $this->getPHIDTransactionNewValue($xaction);
       case PhabricatorTransactions::TYPE_VIEW_POLICY:
       case PhabricatorTransactions::TYPE_EDIT_POLICY:
       case PhabricatorTransactions::TYPE_JOIN_POLICY:
       case PhabricatorTransactions::TYPE_BUILDABLE:
       case PhabricatorTransactions::TYPE_TOKEN:
         return $xaction->getNewValue();
       case PhabricatorTransactions::TYPE_EDGE:
         return $this->getEdgeTransactionNewValue($xaction);
       case PhabricatorTransactions::TYPE_CUSTOMFIELD:
         $field = $this->getCustomFieldForTransaction($object, $xaction);
         return $field->getNewValueFromApplicationTransactions($xaction);
       case PhabricatorTransactions::TYPE_COMMENT:
         return null;
       default:
         return $this->getCustomTransactionNewValue($object, $xaction);
     }
   }
 
   protected function getCustomTransactionOldValue(
     PhabricatorLiskDAO $object,
     PhabricatorApplicationTransaction $xaction) {
     throw new Exception('Capability not supported!');
   }
 
   protected function getCustomTransactionNewValue(
     PhabricatorLiskDAO $object,
     PhabricatorApplicationTransaction $xaction) {
     throw new Exception('Capability not supported!');
   }
 
   protected function transactionHasEffect(
     PhabricatorLiskDAO $object,
     PhabricatorApplicationTransaction $xaction) {
 
     switch ($xaction->getTransactionType()) {
       case PhabricatorTransactions::TYPE_COMMENT:
         return $xaction->hasComment();
       case PhabricatorTransactions::TYPE_CUSTOMFIELD:
         $field = $this->getCustomFieldForTransaction($object, $xaction);
         return $field->getApplicationTransactionHasEffect($xaction);
       case PhabricatorTransactions::TYPE_EDGE:
         // A straight value comparison here doesn't always get the right
         // result, because newly added edges aren't fully populated. Instead,
         // compare the changes in a more granular way.
         $old = $xaction->getOldValue();
         $new = $xaction->getNewValue();
 
         $old_dst = array_keys($old);
         $new_dst = array_keys($new);
 
         // NOTE: For now, we don't consider edge reordering to be a change.
         // We have very few order-dependent edges and effectively no order
         // oriented UI. This might change in the future.
         sort($old_dst);
         sort($new_dst);
 
         if ($old_dst !== $new_dst) {
           // We've added or removed edges, so this transaction definitely
           // has an effect.
           return true;
         }
 
         // We haven't added or removed edges, but we might have changed
         // edge data.
         foreach ($old as $key => $old_value) {
           $new_value = $new[$key];
           if ($old_value['data'] !== $new_value['data']) {
             return true;
           }
         }
 
         return false;
     }
 
     return ($xaction->getOldValue() !== $xaction->getNewValue());
   }
 
   protected function shouldApplyInitialEffects(
     PhabricatorLiskDAO $object,
     array $xactions) {
     return false;
   }
 
   protected function applyInitialEffects(
     PhabricatorLiskDAO $object,
     array $xactions) {
     throw new PhutilMethodNotImplementedException();
   }
 
   private function applyInternalEffects(
     PhabricatorLiskDAO $object,
     PhabricatorApplicationTransaction $xaction) {
 
     switch ($xaction->getTransactionType()) {
       case PhabricatorTransactions::TYPE_BUILDABLE:
       case PhabricatorTransactions::TYPE_TOKEN:
         return;
       case PhabricatorTransactions::TYPE_VIEW_POLICY:
         $object->setViewPolicy($xaction->getNewValue());
         break;
       case PhabricatorTransactions::TYPE_EDIT_POLICY:
         $object->setEditPolicy($xaction->getNewValue());
         break;
       case PhabricatorTransactions::TYPE_CUSTOMFIELD:
         $field = $this->getCustomFieldForTransaction($object, $xaction);
         return $field->applyApplicationTransactionInternalEffects($xaction);
     }
 
     return $this->applyCustomInternalTransaction($object, $xaction);
   }
 
   private function applyExternalEffects(
     PhabricatorLiskDAO $object,
     PhabricatorApplicationTransaction $xaction) {
     switch ($xaction->getTransactionType()) {
       case PhabricatorTransactions::TYPE_BUILDABLE:
       case PhabricatorTransactions::TYPE_TOKEN:
         return;
       case PhabricatorTransactions::TYPE_SUBSCRIBERS:
         $subeditor = id(new PhabricatorSubscriptionsEditor())
           ->setObject($object)
           ->setActor($this->requireActor());
 
         $old_map = array_fuse($xaction->getOldValue());
         $new_map = array_fuse($xaction->getNewValue());
 
         $subeditor->unsubscribe(
           array_keys(
             array_diff_key($old_map, $new_map)));
 
         $subeditor->subscribeExplicit(
           array_keys(
             array_diff_key($new_map, $old_map)));
 
         $subeditor->save();
 
         // for the rest of these edits, subscribers should include those just
         // added as well as those just removed.
         $subscribers = array_unique(array_merge(
           $this->subscribers,
           $xaction->getOldValue(),
           $xaction->getNewValue()));
         $this->subscribers = $subscribers;
 
         break;
       case PhabricatorTransactions::TYPE_EDGE:
         if ($this->getIsInverseEdgeEditor()) {
           // If we're writing an inverse edge transaction, don't actually
           // do anything. The initiating editor on the other side of the
           // transaction will take care of the edge writes.
           break;
         }
 
         $old = $xaction->getOldValue();
         $new = $xaction->getNewValue();
         $src = $object->getPHID();
         $const = $xaction->getMetadataValue('edge:type');
 
         $type = PhabricatorEdgeType::getByConstant($const);
         if ($type->shouldWriteInverseTransactions()) {
           $this->applyInverseEdgeTransactions(
             $object,
             $xaction,
             $type->getInverseEdgeConstant());
         }
 
         foreach ($new as $dst_phid => $edge) {
           $new[$dst_phid]['src'] = $src;
         }
 
         $editor = new PhabricatorEdgeEditor();
 
         foreach ($old as $dst_phid => $edge) {
           if (!empty($new[$dst_phid])) {
             if ($old[$dst_phid]['data'] === $new[$dst_phid]['data']) {
               continue;
             }
           }
           $editor->removeEdge($src, $const, $dst_phid);
         }
 
         foreach ($new as $dst_phid => $edge) {
           if (!empty($old[$dst_phid])) {
             if ($old[$dst_phid]['data'] === $new[$dst_phid]['data']) {
               continue;
             }
           }
 
           $data = array(
             'data' => $edge['data'],
           );
 
           $editor->addEdge($src, $const, $dst_phid, $data);
         }
 
         $editor->save();
         break;
       case PhabricatorTransactions::TYPE_CUSTOMFIELD:
         $field = $this->getCustomFieldForTransaction($object, $xaction);
         return $field->applyApplicationTransactionExternalEffects($xaction);
     }
 
     return $this->applyCustomExternalTransaction($object, $xaction);
   }
 
   protected function applyCustomInternalTransaction(
     PhabricatorLiskDAO $object,
     PhabricatorApplicationTransaction $xaction) {
     $type = $xaction->getTransactionType();
     throw new Exception(
       "Transaction type '{$type}' is missing an internal apply ".
       "implementation!");
   }
 
   protected function applyCustomExternalTransaction(
     PhabricatorLiskDAO $object,
     PhabricatorApplicationTransaction $xaction) {
     $type = $xaction->getTransactionType();
     throw new Exception(
       "Transaction type '{$type}' is missing an external apply ".
       "implementation!");
   }
 
   /**
    * Fill in a transaction's common values, like author and content source.
    */
   protected function populateTransaction(
     PhabricatorLiskDAO $object,
     PhabricatorApplicationTransaction $xaction) {
 
     $actor = $this->getActor();
 
     // TODO: This needs to be more sophisticated once we have meta-policies.
     $xaction->setViewPolicy(PhabricatorPolicies::POLICY_PUBLIC);
 
     if ($actor->isOmnipotent()) {
       $xaction->setEditPolicy(PhabricatorPolicies::POLICY_NOONE);
     } else {
       $xaction->setEditPolicy($this->getActingAsPHID());
     }
 
     $xaction->setAuthorPHID($this->getActingAsPHID());
     $xaction->setContentSource($this->getContentSource());
     $xaction->attachViewer($actor);
     $xaction->attachObject($object);
 
     if ($object->getPHID()) {
       $xaction->setObjectPHID($object->getPHID());
     }
 
     return $xaction;
   }
 
 
   protected function applyFinalEffects(
     PhabricatorLiskDAO $object,
     array $xactions) {
     return $xactions;
   }
 
   public function setContentSource(PhabricatorContentSource $content_source) {
     $this->contentSource = $content_source;
     return $this;
   }
 
   public function setContentSourceFromRequest(AphrontRequest $request) {
     return $this->setContentSource(
       PhabricatorContentSource::newFromRequest($request));
   }
 
   public function setContentSourceFromConduitRequest(
     ConduitAPIRequest $request) {
 
     $content_source = PhabricatorContentSource::newForSource(
       PhabricatorContentSource::SOURCE_CONDUIT,
       array());
 
     return $this->setContentSource($content_source);
   }
 
   public function getContentSource() {
     return $this->contentSource;
   }
 
   final public function applyTransactions(
     PhabricatorLiskDAO $object,
     array $xactions) {
 
     $this->object = $object;
     $this->xactions = $xactions;
     $this->isNewObject = ($object->getPHID() === null);
 
     $this->validateEditParameters($object, $xactions);
 
     $actor = $this->requireActor();
 
     // NOTE: Some transaction expansion requires that the edited object be
     // attached.
     foreach ($xactions as $xaction) {
       $xaction->attachObject($object);
       $xaction->attachViewer($actor);
     }
 
     $xactions = $this->expandTransactions($object, $xactions);
     $xactions = $this->expandSupportTransactions($object, $xactions);
     $xactions = $this->combineTransactions($xactions);
 
     foreach ($xactions as $xaction) {
       $xaction = $this->populateTransaction($object, $xaction);
     }
 
     $is_preview = $this->getIsPreview();
     $read_locking = false;
     $transaction_open = false;
 
     if (!$is_preview) {
       $errors = array();
       $type_map = mgroup($xactions, 'getTransactionType');
       foreach ($this->getTransactionTypes() as $type) {
         $type_xactions = idx($type_map, $type, array());
         $errors[] = $this->validateTransaction($object, $type, $type_xactions);
       }
 
       $errors = array_mergev($errors);
 
       $continue_on_missing = $this->getContinueOnMissingFields();
       foreach ($errors as $key => $error) {
         if ($continue_on_missing && $error->getIsMissingFieldError()) {
           unset($errors[$key]);
         }
       }
 
       if ($errors) {
         throw new PhabricatorApplicationTransactionValidationException($errors);
       }
 
       $file_phids = $this->extractFilePHIDs($object, $xactions);
 
       if ($object->getID()) {
         foreach ($xactions as $xaction) {
 
           // If any of the transactions require a read lock, hold one and
           // reload the object. We need to do this fairly early so that the
           // call to `adjustTransactionValues()` (which populates old values)
           // is based on the synchronized state of the object, which may differ
           // from the state when it was originally loaded.
 
           if ($this->shouldReadLock($object, $xaction)) {
             $object->openTransaction();
             $object->beginReadLocking();
             $transaction_open = true;
             $read_locking = true;
             $object->reload();
             break;
           }
         }
       }
 
       if ($this->shouldApplyInitialEffects($object, $xactions)) {
         if (!$transaction_open) {
           $object->openTransaction();
           $transaction_open = true;
         }
       }
     }
 
     if ($this->shouldApplyInitialEffects($object, $xactions)) {
       $this->applyInitialEffects($object, $xactions);
     }
 
     foreach ($xactions as $xaction) {
       $this->adjustTransactionValues($object, $xaction);
     }
 
     $xactions = $this->filterTransactions($object, $xactions);
 
     if (!$xactions) {
       if ($read_locking) {
         $object->endReadLocking();
         $read_locking = false;
       }
       if ($transaction_open) {
         $object->killTransaction();
         $transaction_open = false;
       }
       return array();
     }
 
     // Now that we've merged, filtered, and combined transactions, check for
     // required capabilities.
     foreach ($xactions as $xaction) {
       $this->requireCapabilities($object, $xaction);
     }
 
     $xactions = $this->sortTransactions($xactions);
 
     if ($is_preview) {
       $this->loadHandles($xactions);
       return $xactions;
     }
 
     $comment_editor = id(new PhabricatorApplicationTransactionCommentEditor())
       ->setActor($actor)
       ->setActingAsPHID($this->getActingAsPHID())
       ->setContentSource($this->getContentSource());
 
     if (!$transaction_open) {
       $object->openTransaction();
     }
 
       foreach ($xactions as $xaction) {
         $this->applyInternalEffects($object, $xaction);
       }
 
       $object->save();
 
       foreach ($xactions as $xaction) {
         $xaction->setObjectPHID($object->getPHID());
         if ($xaction->getComment()) {
           $xaction->setPHID($xaction->generatePHID());
           $comment_editor->applyEdit($xaction, $xaction->getComment());
         } else {
           $xaction->save();
         }
       }
 
       if ($file_phids) {
         $this->attachFiles($object, $file_phids);
       }
 
       foreach ($xactions as $xaction) {
         $this->applyExternalEffects($object, $xaction);
       }
 
       $xactions = $this->applyFinalEffects($object, $xactions);
 
       if ($read_locking) {
         $object->endReadLocking();
         $read_locking = false;
       }
 
     $object->saveTransaction();
 
     // Now that we've completely applied the core transaction set, try to apply
     // Herald rules. Herald rules are allowed to either take direct actions on
     // the database (like writing flags), or take indirect actions (like saving
     // some targets for CC when we generate mail a little later), or return
     // transactions which we'll apply normally using another Editor.
 
     // First, check if *this* is a sub-editor which is itself applying Herald
     // rules: if it is, stop working and return so we don't descend into
     // madness.
 
     // Otherwise, we're not a Herald editor, so process Herald rules (possibly
     // using a Herald editor to apply resulting transactions) and then send out
     // mail, notifications, and feed updates about everything.
 
     if ($this->getIsHeraldEditor()) {
       // We are the Herald editor, so stop work here and return the updated
       // transactions.
       return $xactions;
     } else if ($this->shouldApplyHeraldRules($object, $xactions)) {
       // We are not the Herald editor, so try to apply Herald rules.
       $herald_xactions = $this->applyHeraldRules($object, $xactions);
 
       if ($herald_xactions) {
         $xscript_id = $this->getHeraldTranscript()->getID();
         foreach ($herald_xactions as $herald_xaction) {
           $herald_xaction->setMetadataValue('herald:transcriptID', $xscript_id);
         }
 
         // NOTE: We're acting as the omnipotent user because rules deal with
         // their own policy issues. We use a synthetic author PHID (the
         // Herald application) as the author of record, so that transactions
         // will render in a reasonable way ("Herald assigned this task ...").
         $herald_actor = PhabricatorUser::getOmnipotentUser();
         $herald_phid = id(new PhabricatorHeraldApplication())->getPHID();
 
         // TODO: It would be nice to give transactions a more specific source
         // which points at the rule which generated them. You can figure this
         // out from transcripts, but it would be cleaner if you didn't have to.
 
         $herald_source = PhabricatorContentSource::newForSource(
           PhabricatorContentSource::SOURCE_HERALD,
           array());
 
         $herald_editor = newv(get_class($this), array())
           ->setContinueOnNoEffect(true)
           ->setContinueOnMissingFields(true)
           ->setParentMessageID($this->getParentMessageID())
           ->setIsHeraldEditor(true)
           ->setActor($herald_actor)
           ->setActingAsPHID($herald_phid)
           ->setContentSource($herald_source);
 
         $herald_xactions = $herald_editor->applyTransactions(
           $object,
           $herald_xactions);
 
         // Merge the new transactions into the transaction list: we want to
         // send email and publish feed stories about them, too.
         $xactions = array_merge($xactions, $herald_xactions);
       }
     }
 
     // Before sending mail or publishing feed stories, reload the object
     // subscribers to pick up changes caused by Herald (or by other side effects
     // in various transaction phases).
     $this->loadSubscribers($object);
 
     $this->loadHandles($xactions);
 
     $mail = null;
     if (!$this->getDisableEmail()) {
       if ($this->shouldSendMail($object, $xactions)) {
         $mail = $this->sendMail($object, $xactions);
       }
     }
 
     if ($this->supportsSearch()) {
       id(new PhabricatorSearchIndexer())
         ->queueDocumentForIndexing($object->getPHID());
     }
 
     if ($this->shouldPublishFeedStory($object, $xactions)) {
       $mailed = array();
       if ($mail) {
         $mailed = $mail->buildRecipientList();
       }
       $this->publishFeedStory(
         $object,
         $xactions,
         $mailed);
     }
 
     $this->didApplyTransactions($xactions);
 
     if ($object instanceof PhabricatorCustomFieldInterface) {
       // Maybe this makes more sense to move into the search index itself? For
       // now I'm putting it here since I think we might end up with things that
       // need it to be up to date once the next page loads, but if we don't go
       // there we we could move it into search once search moves to the daemons.
 
       // It now happens in the search indexer as well, but the search indexer is
       // always daemonized, so the logic above still potentially holds. We could
       // possibly get rid of this. The major motivation for putting it in the
       // indexer was to enable reindexing to work.
 
       $fields = PhabricatorCustomField::getObjectFields(
         $object,
         PhabricatorCustomField::ROLE_APPLICATIONSEARCH);
       $fields->readFieldsFromStorage($object);
       $fields->rebuildIndexes($object);
     }
 
     return $xactions;
   }
 
   protected function didApplyTransactions(array $xactions) {
     // Hook for subclasses.
     return;
   }
 
 
   /**
    * Determine if the editor should hold a read lock on the object while
    * applying a transaction.
    *
    * If the editor does not hold a lock, two editors may read an object at the
    * same time, then apply their changes without any synchronization. For most
    * transactions, this does not matter much. However, it is important for some
    * transactions. For example, if an object has a transaction count on it, both
    * editors may read the object with `count = 23`, then independently update it
    * and save the object with `count = 24` twice. This will produce the wrong
    * state: the object really has 25 transactions, but the count is only 24.
    *
    * Generally, transactions fall into one of four buckets:
    *
    *   - Append operations: Actions like adding a comment to an object purely
    *     add information to its state, and do not depend on the current object
    *     state in any way. These transactions never need to hold locks.
    *   - Overwrite operations: Actions like changing the title or description
    *     of an object replace the current value with a new value, so the end
    *     state is consistent without a lock. We currently do not lock these
    *     transactions, although we may in the future.
    *   - Edge operations: Edge and subscription operations have internal
    *     synchronization which limits the damage race conditions can cause.
    *     We do not currently lock these transactions, although we may in the
    *     future.
    *   - Update operations: Actions like incrementing a count on an object.
    *     These operations generally should use locks, unless it is not
    *     important that the state remain consistent in the presence of races.
    *
    * @param   PhabricatorLiskDAO  Object being updated.
    * @param   PhabricatorApplicationTransaction Transaction being applied.
    * @return  bool                True to synchronize the edit with a lock.
    */
   protected function shouldReadLock(
     PhabricatorLiskDAO $object,
     PhabricatorApplicationTransaction $xaction) {
     return false;
   }
 
   private function loadHandles(array $xactions) {
     $phids = array();
     foreach ($xactions as $key => $xaction) {
       $phids[$key] = $xaction->getRequiredHandlePHIDs();
     }
     $handles = array();
     $merged = array_mergev($phids);
     if ($merged) {
       $handles = id(new PhabricatorHandleQuery())
         ->setViewer($this->requireActor())
         ->withPHIDs($merged)
         ->execute();
     }
     foreach ($xactions as $key => $xaction) {
       $xaction->setHandles(array_select_keys($handles, $phids[$key]));
     }
   }
 
   private function loadSubscribers(PhabricatorLiskDAO $object) {
     if ($object->getPHID() &&
         ($object instanceof PhabricatorSubscribableInterface)) {
       $subs = PhabricatorSubscribersQuery::loadSubscribersForPHID(
         $object->getPHID());
       $this->subscribers = array_fuse($subs);
     } else {
       $this->subscribers = array();
     }
   }
 
   private function validateEditParameters(
     PhabricatorLiskDAO $object,
     array $xactions) {
 
     if (!$this->getContentSource()) {
       throw new Exception(
         'Call setContentSource() before applyTransactions()!');
     }
 
     // Do a bunch of sanity checks that the incoming transactions are fresh.
     // They should be unsaved and have only "transactionType" and "newValue"
     // set.
 
     $types = array_fill_keys($this->getTransactionTypes(), true);
 
     assert_instances_of($xactions, 'PhabricatorApplicationTransaction');
     foreach ($xactions as $xaction) {
       if ($xaction->getPHID() || $xaction->getID()) {
         throw new PhabricatorApplicationTransactionStructureException(
           $xaction,
           pht(
             'You can not apply transactions which already have IDs/PHIDs!'));
       }
       if ($xaction->getObjectPHID()) {
         throw new PhabricatorApplicationTransactionStructureException(
           $xaction,
           pht(
             'You can not apply transactions which already have objectPHIDs!'));
       }
       if ($xaction->getAuthorPHID()) {
         throw new PhabricatorApplicationTransactionStructureException(
           $xaction,
           pht(
             'You can not apply transactions which already have authorPHIDs!'));
       }
       if ($xaction->getCommentPHID()) {
         throw new PhabricatorApplicationTransactionStructureException(
           $xaction,
           pht(
             'You can not apply transactions which already have '.
             'commentPHIDs!'));
       }
       if ($xaction->getCommentVersion() !== 0) {
         throw new PhabricatorApplicationTransactionStructureException(
           $xaction,
           pht(
             'You can not apply transactions which already have '.
             'commentVersions!'));
       }
 
       $expect_value = !$xaction->shouldGenerateOldValue();
       $has_value = $xaction->hasOldValue();
 
       if ($expect_value && !$has_value) {
         throw new PhabricatorApplicationTransactionStructureException(
           $xaction,
           pht(
             'This transaction is supposed to have an oldValue set, but '.
             'it does not!'));
       }
 
       if ($has_value && !$expect_value) {
         throw new PhabricatorApplicationTransactionStructureException(
           $xaction,
           pht(
             'This transaction should generate its oldValue automatically, '.
             'but has already had one set!'));
       }
 
       $type = $xaction->getTransactionType();
       if (empty($types[$type])) {
         throw new PhabricatorApplicationTransactionStructureException(
           $xaction,
           pht(
             'Transaction has type "%s", but that transaction type is not '.
             'supported by this editor (%s).',
             $type,
             get_class($this)));
       }
     }
   }
 
   protected function requireCapabilities(
     PhabricatorLiskDAO $object,
     PhabricatorApplicationTransaction $xaction) {
 
     if ($this->getIsNewObject()) {
       return;
     }
 
     $actor = $this->requireActor();
     switch ($xaction->getTransactionType()) {
       case PhabricatorTransactions::TYPE_COMMENT:
         PhabricatorPolicyFilter::requireCapability(
           $actor,
           $object,
           PhabricatorPolicyCapability::CAN_VIEW);
         break;
       case PhabricatorTransactions::TYPE_VIEW_POLICY:
         PhabricatorPolicyFilter::requireCapability(
           $actor,
           $object,
           PhabricatorPolicyCapability::CAN_EDIT);
         break;
       case PhabricatorTransactions::TYPE_EDIT_POLICY:
         PhabricatorPolicyFilter::requireCapability(
           $actor,
           $object,
           PhabricatorPolicyCapability::CAN_EDIT);
         break;
       case PhabricatorTransactions::TYPE_JOIN_POLICY:
         PhabricatorPolicyFilter::requireCapability(
           $actor,
           $object,
           PhabricatorPolicyCapability::CAN_EDIT);
         break;
     }
   }
 
   private function buildMentionTransaction(
     PhabricatorLiskDAO $object,
     array $xactions,
     array $blocks) {
 
     if (!($object instanceof PhabricatorSubscribableInterface)) {
       return null;
     }
 
     $texts = array_mergev($blocks);
     $phids = PhabricatorMarkupEngine::extractPHIDsFromMentions(
       $this->getActor(),
       $texts);
 
     $this->mentionedPHIDs = $phids;
 
     if ($object->getPHID()) {
       // Don't try to subscribe already-subscribed mentions: we want to generate
       // a dialog about an action having no effect if the user explicitly adds
       // existing CCs, but not if they merely mention existing subscribers.
       $phids = array_diff($phids, $this->subscribers);
     }
 
     foreach ($phids as $key => $phid) {
       if ($object->isAutomaticallySubscribed($phid)) {
         unset($phids[$key]);
       }
     }
     $phids = array_values($phids);
 
     if (!$phids) {
       return null;
     }
 
     $xaction = newv(get_class(head($xactions)), array());
     $xaction->setTransactionType(PhabricatorTransactions::TYPE_SUBSCRIBERS);
     $xaction->setNewValue(array('+' => $phids));
 
     return $xaction;
   }
 
   protected function getRemarkupBlocksFromTransaction(
     PhabricatorApplicationTransaction $transaction) {
     return $transaction->getRemarkupBlocks();
   }
 
   protected function mergeTransactions(
     PhabricatorApplicationTransaction $u,
     PhabricatorApplicationTransaction $v) {
 
     $type = $u->getTransactionType();
 
     switch ($type) {
       case PhabricatorTransactions::TYPE_SUBSCRIBERS:
         return $this->mergePHIDOrEdgeTransactions($u, $v);
       case PhabricatorTransactions::TYPE_EDGE:
         $u_type = $u->getMetadataValue('edge:type');
         $v_type = $v->getMetadataValue('edge:type');
         if ($u_type == $v_type) {
           return $this->mergePHIDOrEdgeTransactions($u, $v);
         }
         return null;
     }
 
     // By default, do not merge the transactions.
     return null;
   }
 
   /**
    * Optionally expand transactions which imply other effects. For example,
    * resigning from a revision in Differential implies removing yourself as
    * a reviewer.
    */
   private function expandTransactions(
     PhabricatorLiskDAO $object,
     array $xactions) {
 
     $results = array();
     foreach ($xactions as $xaction) {
       foreach ($this->expandTransaction($object, $xaction) as $expanded) {
         $results[] = $expanded;
       }
     }
 
     return $results;
   }
 
   protected function expandTransaction(
     PhabricatorLiskDAO $object,
     PhabricatorApplicationTransaction $xaction) {
     return array($xaction);
   }
 
 
   private function expandSupportTransactions(
     PhabricatorLiskDAO $object,
     array $xactions) {
     $this->loadSubscribers($object);
 
     $xactions = $this->applyImplicitCC($object, $xactions);
 
     $blocks = array();
     foreach ($xactions as $key => $xaction) {
       $blocks[$key] = $this->getRemarkupBlocksFromTransaction($xaction);
     }
 
     $mention_xaction = $this->buildMentionTransaction(
       $object,
       $xactions,
       $blocks);
     if ($mention_xaction) {
       $xactions[] = $mention_xaction;
     }
 
     // TODO: For now, this is just a placeholder.
     $engine = PhabricatorMarkupEngine::getEngine('extract');
     $engine->setConfig('viewer', $this->requireActor());
 
     $block_xactions = $this->expandRemarkupBlockTransactions(
       $object,
       $xactions,
       $blocks,
       $engine);
 
     foreach ($block_xactions as $xaction) {
       $xactions[] = $xaction;
     }
 
     return $xactions;
   }
 
   private function expandRemarkupBlockTransactions(
     PhabricatorLiskDAO $object,
     array $xactions,
     $blocks,
     PhutilMarkupEngine $engine) {
 
     $block_xactions = $this->expandCustomRemarkupBlockTransactions(
       $object,
       $xactions,
       $blocks,
       $engine);
 
     if ($object instanceof PhabricatorProjectInterface) {
       $phids = array();
       foreach ($blocks as $key => $xaction_blocks) {
         foreach ($xaction_blocks as $block) {
           $engine->markupText($block);
           $phids += $engine->getTextMetadata(
             PhabricatorObjectRemarkupRule::KEY_MENTIONED_OBJECTS,
             array());
         }
       }
 
       $project_type = PhabricatorProjectProjectPHIDType::TYPECONST;
       foreach ($phids as $key => $phid) {
         if (phid_get_type($phid) != $project_type) {
           unset($phids[$key]);
         }
       }
 
       if ($phids) {
         $edge_type = PhabricatorProjectObjectHasProjectEdgeType::EDGECONST;
         $block_xactions[] = newv(get_class(head($xactions)), array())
           ->setIgnoreOnNoEffect(true)
           ->setTransactionType(PhabricatorTransactions::TYPE_EDGE)
           ->setMetadataValue('edge:type', $edge_type)
           ->setNewValue(array('+' => $phids));
       }
     }
 
     return $block_xactions;
   }
 
   protected function expandCustomRemarkupBlockTransactions(
     PhabricatorLiskDAO $object,
     array $xactions,
     $blocks,
     PhutilMarkupEngine $engine) {
     return array();
   }
 
 
   /**
    * Attempt to combine similar transactions into a smaller number of total
    * transactions. For example, two transactions which edit the title of an
    * object can be merged into a single edit.
    */
   private function combineTransactions(array $xactions) {
     $stray_comments = array();
 
     $result = array();
     $types = array();
     foreach ($xactions as $key => $xaction) {
       $type = $xaction->getTransactionType();
       if (isset($types[$type])) {
         foreach ($types[$type] as $other_key) {
           $merged = $this->mergeTransactions($result[$other_key], $xaction);
           if ($merged) {
             $result[$other_key] = $merged;
 
             if ($xaction->getComment() &&
                 ($xaction->getComment() !== $merged->getComment())) {
               $stray_comments[] = $xaction->getComment();
             }
 
             if ($result[$other_key]->getComment() &&
                 ($result[$other_key]->getComment() !== $merged->getComment())) {
               $stray_comments[] = $result[$other_key]->getComment();
             }
 
             // Move on to the next transaction.
             continue 2;
           }
         }
       }
       $result[$key] = $xaction;
       $types[$type][] = $key;
     }
 
     // If we merged any comments away, restore them.
     foreach ($stray_comments as $comment) {
       $xaction = newv(get_class(head($result)), array());
       $xaction->setTransactionType(PhabricatorTransactions::TYPE_COMMENT);
       $xaction->setComment($comment);
       $result[] = $xaction;
     }
 
     return array_values($result);
   }
 
   protected function mergePHIDOrEdgeTransactions(
     PhabricatorApplicationTransaction $u,
     PhabricatorApplicationTransaction $v) {
 
     $result = $u->getNewValue();
     foreach ($v->getNewValue() as $key => $value) {
       if ($u->getTransactionType() == PhabricatorTransactions::TYPE_EDGE) {
         if (empty($result[$key])) {
           $result[$key] = $value;
         } else {
           // We're merging two lists of edge adds, sets, or removes. Merge
           // them by merging individual PHIDs within them.
           $merged = $result[$key];
 
           foreach ($value as $dst => $v_spec) {
             if (empty($merged[$dst])) {
               $merged[$dst] = $v_spec;
             } else {
               // Two transactions are trying to perform the same operation on
               // the same edge. Normalize the edge data and then merge it. This
               // allows transactions to specify how data merges execute in a
               // precise way.
 
               $u_spec = $merged[$dst];
 
               if (!is_array($u_spec)) {
                 $u_spec = array('dst' => $u_spec);
               }
               if (!is_array($v_spec)) {
                 $v_spec = array('dst' => $v_spec);
               }
 
               $ux_data = idx($u_spec, 'data', array());
               $vx_data = idx($v_spec, 'data', array());
 
               $merged_data = $this->mergeEdgeData(
                 $u->getMetadataValue('edge:type'),
                 $ux_data,
                 $vx_data);
 
               $u_spec['data'] = $merged_data;
               $merged[$dst] = $u_spec;
             }
           }
 
           $result[$key] = $merged;
         }
       } else {
         $result[$key] = array_merge($value, idx($result, $key, array()));
       }
     }
     $u->setNewValue($result);
 
     // When combining an "ignore" transaction with a normal transaction, make
     // sure we don't propagate the "ignore" flag.
     if (!$v->getIgnoreOnNoEffect()) {
       $u->setIgnoreOnNoEffect(false);
     }
 
     return $u;
   }
 
   protected function mergeEdgeData($type, array $u, array $v) {
     return $v + $u;
   }
 
   protected function getPHIDTransactionNewValue(
     PhabricatorApplicationTransaction $xaction) {
 
     $old = array_fuse($xaction->getOldValue());
 
     $new = $xaction->getNewValue();
     $new_add = idx($new, '+', array());
     unset($new['+']);
     $new_rem = idx($new, '-', array());
     unset($new['-']);
     $new_set = idx($new, '=', null);
     if ($new_set !== null) {
       $new_set = array_fuse($new_set);
     }
     unset($new['=']);
 
     if ($new) {
       throw new Exception(
         "Invalid 'new' value for PHID transaction. Value should contain only ".
         "keys '+' (add PHIDs), '-' (remove PHIDs) and '=' (set PHIDS).");
     }
 
     $result = array();
 
     foreach ($old as $phid) {
       if ($new_set !== null && empty($new_set[$phid])) {
         continue;
       }
       $result[$phid] = $phid;
     }
 
     if ($new_set !== null) {
       foreach ($new_set as $phid) {
         $result[$phid] = $phid;
       }
     }
 
     foreach ($new_add as $phid) {
       $result[$phid] = $phid;
     }
 
     foreach ($new_rem as $phid) {
       unset($result[$phid]);
     }
 
     return array_values($result);
   }
 
   protected function getEdgeTransactionNewValue(
     PhabricatorApplicationTransaction $xaction) {
 
     $new = $xaction->getNewValue();
     $new_add = idx($new, '+', array());
     unset($new['+']);
     $new_rem = idx($new, '-', array());
     unset($new['-']);
     $new_set = idx($new, '=', null);
     unset($new['=']);
 
     if ($new) {
       throw new Exception(
         "Invalid 'new' value for Edge transaction. Value should contain only ".
         "keys '+' (add edges), '-' (remove edges) and '=' (set edges).");
     }
 
     $old = $xaction->getOldValue();
 
     $lists = array($new_set, $new_add, $new_rem);
     foreach ($lists as $list) {
       $this->checkEdgeList($list);
     }
 
     $result = array();
     foreach ($old as $dst_phid => $edge) {
       if ($new_set !== null && empty($new_set[$dst_phid])) {
         continue;
       }
       $result[$dst_phid] = $this->normalizeEdgeTransactionValue(
         $xaction,
         $edge,
         $dst_phid);
     }
 
     if ($new_set !== null) {
       foreach ($new_set as $dst_phid => $edge) {
         $result[$dst_phid] = $this->normalizeEdgeTransactionValue(
           $xaction,
           $edge,
           $dst_phid);
       }
     }
 
     foreach ($new_add as $dst_phid => $edge) {
       $result[$dst_phid] = $this->normalizeEdgeTransactionValue(
         $xaction,
         $edge,
         $dst_phid);
     }
 
     foreach ($new_rem as $dst_phid => $edge) {
       unset($result[$dst_phid]);
     }
 
     return $result;
   }
 
   private function checkEdgeList($list) {
     if (!$list) {
       return;
     }
     foreach ($list as $key => $item) {
       if (phid_get_type($key) === PhabricatorPHIDConstants::PHID_TYPE_UNKNOWN) {
         throw new Exception(
           "Edge transactions must have destination PHIDs as in edge ".
           "lists (found key '{$key}').");
       }
       if (!is_array($item) && $item !== $key) {
         throw new Exception(
           "Edge transactions must have PHIDs or edge specs as values ".
           "(found value '{$item}').");
       }
     }
   }
 
   private function normalizeEdgeTransactionValue(
     PhabricatorApplicationTransaction $xaction,
     $edge,
     $dst_phid) {
 
     if (!is_array($edge)) {
       if ($edge != $dst_phid) {
         throw new Exception(
           pht(
             'Transaction edge data must either be the edge PHID or an edge '.
             'specification dictionary.'));
       }
       $edge = array();
     } else {
       foreach ($edge as $key => $value) {
         switch ($key) {
           case 'src':
           case 'dst':
           case 'type':
           case 'data':
           case 'dateCreated':
           case 'dateModified':
           case 'seq':
           case 'dataID':
             break;
           default:
             throw new Exception(
               pht(
                 'Transaction edge specification contains unexpected key '.
                 '"%s".',
                 $key));
         }
       }
     }
 
     $edge['dst'] = $dst_phid;
 
     $edge_type = $xaction->getMetadataValue('edge:type');
     if (empty($edge['type'])) {
       $edge['type'] = $edge_type;
     } else {
       if ($edge['type'] != $edge_type) {
         $this_type = $edge['type'];
         throw new Exception(
           "Edge transaction includes edge of type '{$this_type}', but ".
           "transaction is of type '{$edge_type}'. Each edge transaction must ".
           "alter edges of only one type.");
       }
     }
 
     if (!isset($edge['data'])) {
       $edge['data'] = array();
     }
 
     return $edge;
   }
 
   protected function sortTransactions(array $xactions) {
     $head = array();
     $tail = array();
 
     // Move bare comments to the end, so the actions precede them.
     foreach ($xactions as $xaction) {
       $type = $xaction->getTransactionType();
       if ($type == PhabricatorTransactions::TYPE_COMMENT) {
         $tail[] = $xaction;
       } else {
         $head[] = $xaction;
       }
     }
 
     return array_values(array_merge($head, $tail));
   }
 
 
   protected function filterTransactions(
     PhabricatorLiskDAO $object,
     array $xactions) {
 
     $type_comment = PhabricatorTransactions::TYPE_COMMENT;
 
     $no_effect = array();
     $has_comment = false;
     $any_effect = false;
     foreach ($xactions as $key => $xaction) {
       if ($this->transactionHasEffect($object, $xaction)) {
         if ($xaction->getTransactionType() != $type_comment) {
           $any_effect = true;
         }
       } else if ($xaction->getIgnoreOnNoEffect()) {
         unset($xactions[$key]);
       } else {
         $no_effect[$key] = $xaction;
       }
       if ($xaction->hasComment()) {
         $has_comment = true;
       }
     }
 
     if (!$no_effect) {
       return $xactions;
     }
 
     if (!$this->getContinueOnNoEffect() && !$this->getIsPreview()) {
       throw new PhabricatorApplicationTransactionNoEffectException(
         $no_effect,
         $any_effect,
         $has_comment);
     }
 
     if (!$any_effect && !$has_comment) {
       // If we only have empty comment transactions, just drop them all.
       return array();
     }
 
     foreach ($no_effect as $key => $xaction) {
       if ($xaction->getComment()) {
         $xaction->setTransactionType($type_comment);
         $xaction->setOldValue(null);
         $xaction->setNewValue(null);
       } else {
         unset($xactions[$key]);
       }
     }
 
     return $xactions;
   }
 
 
   /**
    * Hook for validating transactions. This callback will be invoked for each
    * available transaction type, even if an edit does not apply any transactions
    * of that type. This allows you to raise exceptions when required fields are
    * missing, by detecting that the object has no field value and there is no
    * transaction which sets one.
    *
    * @param PhabricatorLiskDAO Object being edited.
    * @param string Transaction type to validate.
    * @param list<PhabricatorApplicationTransaction> Transactions of given type,
    *   which may be empty if the edit does not apply any transactions of the
    *   given type.
    * @return list<PhabricatorApplicationTransactionValidationError> List of
    *   validation errors.
    */
   protected function validateTransaction(
     PhabricatorLiskDAO $object,
     $type,
     array $xactions) {
 
     $errors = array();
     switch ($type) {
       case PhabricatorTransactions::TYPE_VIEW_POLICY:
         $errors[] = $this->validatePolicyTransaction(
           $object,
           $xactions,
           $type,
           PhabricatorPolicyCapability::CAN_VIEW);
         break;
       case PhabricatorTransactions::TYPE_EDIT_POLICY:
         $errors[] = $this->validatePolicyTransaction(
           $object,
           $xactions,
           $type,
           PhabricatorPolicyCapability::CAN_EDIT);
         break;
       case PhabricatorTransactions::TYPE_CUSTOMFIELD:
         $groups = array();
         foreach ($xactions as $xaction) {
           $groups[$xaction->getMetadataValue('customfield:key')][] = $xaction;
         }
 
         $field_list = PhabricatorCustomField::getObjectFields(
           $object,
           PhabricatorCustomField::ROLE_EDIT);
         $field_list->setViewer($this->getActor());
 
         $role_xactions = PhabricatorCustomField::ROLE_APPLICATIONTRANSACTIONS;
         foreach ($field_list->getFields() as $field) {
           if (!$field->shouldEnableForRole($role_xactions)) {
             continue;
           }
           $errors[] = $field->validateApplicationTransactions(
             $this,
             $type,
             idx($groups, $field->getFieldKey(), array()));
         }
         break;
     }
 
     return array_mergev($errors);
   }
 
   private function validatePolicyTransaction(
     PhabricatorLiskDAO $object,
     array $xactions,
     $transaction_type,
     $capability) {
 
     $actor = $this->requireActor();
     $errors = array();
     // Note $this->xactions is necessary; $xactions is $this->xactions of
     // $transaction_type
     $policy_object = $this->adjustObjectForPolicyChecks(
       $object,
       $this->xactions);
 
     // Make sure the user isn't editing away their ability to $capability this
     // object.
     foreach ($xactions as $xaction) {
       try {
         PhabricatorPolicyFilter::requireCapabilityWithForcedPolicy(
           $actor,
           $policy_object,
           $capability,
           $xaction->getNewValue());
       } catch (PhabricatorPolicyException $ex) {
         $errors[] = new PhabricatorApplicationTransactionValidationError(
           $transaction_type,
           pht('Invalid'),
           pht(
             'You can not select this %s policy, because you would no longer '.
             'be able to %s the object.',
             $capability,
             $capability),
           $xaction);
       }
     }
 
     if ($this->getIsNewObject()) {
       if (!$xactions) {
         $has_capability = PhabricatorPolicyFilter::hasCapability(
           $actor,
           $policy_object,
           $capability);
         if (!$has_capability) {
           $errors[] = new PhabricatorApplicationTransactionValidationError(
             $transaction_type,
             pht('Invalid'),
             pht('The selected %s policy excludes you. Choose a %s policy '.
                 'which allows you to %s the object.',
             $capability,
             $capability,
             $capability));
         }
       }
     }
 
     return $errors;
   }
 
   protected function adjustObjectForPolicyChecks(
     PhabricatorLiskDAO $object,
     array $xactions) {
 
     return clone $object;
   }
 
   /**
    * Check for a missing text field.
    *
    * A text field is missing if the object has no value and there are no
    * transactions which set a value, or if the transactions remove the value.
    * This method is intended to make implementing @{method:validateTransaction}
    * more convenient:
    *
    *   $missing = $this->validateIsEmptyTextField(
    *     $object->getName(),
    *     $xactions);
    *
    * This will return `true` if the net effect of the object and transactions
    * is an empty field.
    *
    * @param wild Current field value.
    * @param list<PhabricatorApplicationTransaction> Transactions editing the
    *          field.
    * @return bool True if the field will be an empty text field after edits.
    */
   protected function validateIsEmptyTextField($field_value, array $xactions) {
     if (strlen($field_value) && empty($xactions)) {
       return false;
     }
 
     if ($xactions && strlen(last($xactions)->getNewValue())) {
       return false;
     }
 
     return true;
   }
 
 
 /* -(  Implicit CCs  )------------------------------------------------------- */
 
 
   /**
    * When a user interacts with an object, we might want to add them to CC.
    */
   final public function applyImplicitCC(
     PhabricatorLiskDAO $object,
     array $xactions) {
 
     if (!($object instanceof PhabricatorSubscribableInterface)) {
       // If the object isn't subscribable, we can't CC them.
       return $xactions;
     }
 
     $actor_phid = $this->getActingAsPHID();
 
     $type_user = PhabricatorPeopleUserPHIDType::TYPECONST;
     if (phid_get_type($actor_phid) != $type_user) {
       // Transactions by application actors like Herald, Harbormaster and
       // Diffusion should not CC the applications.
       return $xactions;
     }
 
     if ($object->isAutomaticallySubscribed($actor_phid)) {
       // If they're auto-subscribed, don't CC them.
       return $xactions;
     }
 
     $should_cc = false;
     foreach ($xactions as $xaction) {
       if ($this->shouldImplyCC($object, $xaction)) {
         $should_cc = true;
         break;
       }
     }
 
     if (!$should_cc) {
       // Only some types of actions imply a CC (like adding a comment).
       return $xactions;
     }
 
     if ($object->getPHID()) {
       if (isset($this->subscribers[$actor_phid])) {
         // If the user is already subscribed, don't implicitly CC them.
         return $xactions;
       }
 
       $unsub = PhabricatorEdgeQuery::loadDestinationPHIDs(
         $object->getPHID(),
         PhabricatorEdgeConfig::TYPE_OBJECT_HAS_UNSUBSCRIBER);
       $unsub = array_fuse($unsub);
       if (isset($unsub[$actor_phid])) {
         // If the user has previously unsubscribed from this object explicitly,
         // don't implicitly CC them.
         return $xactions;
       }
     }
 
     $xaction = newv(get_class(head($xactions)), array());
     $xaction->setTransactionType(PhabricatorTransactions::TYPE_SUBSCRIBERS);
     $xaction->setNewValue(array('+' => array($actor_phid)));
 
     array_unshift($xactions, $xaction);
 
     return $xactions;
   }
 
   protected function shouldImplyCC(
     PhabricatorLiskDAO $object,
     PhabricatorApplicationTransaction $xaction) {
 
     return $xaction->isCommentTransaction();
   }
 
 
 /* -(  Sending Mail  )------------------------------------------------------- */
 
 
   /**
    * @task mail
    */
   protected function shouldSendMail(
     PhabricatorLiskDAO $object,
     array $xactions) {
     return false;
   }
 
 
   /**
    * @task mail
    */
   protected function sendMail(
     PhabricatorLiskDAO $object,
     array $xactions) {
 
     // Check if any of the transactions are visible. If we don't have any
     // visible transactions, don't send the mail.
 
     $any_visible = false;
     foreach ($xactions as $xaction) {
       if (!$xaction->shouldHideForMail($xactions)) {
         $any_visible = true;
         break;
       }
     }
 
     if (!$any_visible) {
       return;
     }
 
     $email_to = array_filter(array_unique($this->getMailTo($object)));
     $email_cc = array_filter(array_unique($this->getMailCC($object)));
 
     $phids = array_merge($email_to, $email_cc);
     $handles = id(new PhabricatorHandleQuery())
       ->setViewer($this->requireActor())
       ->withPHIDs($phids)
       ->execute();
 
     $template = $this->buildMailTemplate($object);
     $body = $this->buildMailBody($object, $xactions);
 
     $mail_tags = $this->getMailTags($object, $xactions);
     $action = $this->getMailAction($object, $xactions);
 
     $reply_handler = $this->buildReplyHandler($object);
     $reply_section = $reply_handler->getReplyHandlerInstructions();
     if ($reply_section !== null) {
       $body->addReplySection($reply_section);
     }
 
     $template
       ->setFrom($this->getActingAsPHID())
       ->setSubjectPrefix($this->getMailSubjectPrefix())
       ->setVarySubjectPrefix('['.$action.']')
       ->setThreadID($this->getMailThreadID($object), $this->getIsNewObject())
       ->setRelatedPHID($object->getPHID())
       ->setExcludeMailRecipientPHIDs($this->getExcludeMailRecipientPHIDs())
       ->setMailTags($mail_tags)
       ->setIsBulk(true)
       ->setBody($body->render());
 
     foreach ($body->getAttachments() as $attachment) {
       $template->addAttachment($attachment);
     }
 
     $herald_xscript = $this->getHeraldTranscript();
     if ($herald_xscript) {
       $herald_header = $herald_xscript->getXHeraldRulesHeader();
       $herald_header = HeraldTranscript::saveXHeraldRulesHeader(
         $object->getPHID(),
         $herald_header);
     } else {
       $herald_header = HeraldTranscript::loadXHeraldRulesHeader(
         $object->getPHID());
     }
 
     if ($herald_header) {
       $template->addHeader('X-Herald-Rules', $herald_header);
     }
 
     if ($this->getParentMessageID()) {
       $template->setParentMessageID($this->getParentMessageID());
     }
 
     $mails = $reply_handler->multiplexMail(
         $template,
         array_select_keys($handles, $email_to),
         array_select_keys($handles, $email_cc));
 
     foreach ($mails as $mail) {
       $mail->saveAndSend();
     }
 
     $template->addTos($email_to);
     $template->addCCs($email_cc);
 
     return $template;
   }
 
   protected function getMailThreadID(PhabricatorLiskDAO $object) {
     return $object->getPHID();
   }
 
 
   /**
    * @task mail
    */
   protected function getStrongestAction(
     PhabricatorLiskDAO $object,
     array $xactions) {
     return last(msort($xactions, 'getActionStrength'));
   }
 
 
   /**
    * @task mail
    */
   protected function buildReplyHandler(PhabricatorLiskDAO $object) {
     throw new Exception('Capability not supported.');
   }
 
 
   /**
    * @task mail
    */
   protected function getMailSubjectPrefix() {
     throw new Exception('Capability not supported.');
   }
 
 
   /**
    * @task mail
    */
   protected function getMailTags(
     PhabricatorLiskDAO $object,
     array $xactions) {
     $tags = array();
 
     foreach ($xactions as $xaction) {
       $tags[] = $xaction->getMailTags();
     }
 
     return array_mergev($tags);
   }
 
   /**
    * @task mail
    */
   public function getMailTagsMap() {
     // TODO: We should move shared mail tags, like "comment", here.
     return array();
   }
 
 
   /**
    * @task mail
    */
   protected function getMailAction(
     PhabricatorLiskDAO $object,
     array $xactions) {
     return $this->getStrongestAction($object, $xactions)->getActionName();
   }
 
 
   /**
    * @task mail
    */
   protected function buildMailTemplate(PhabricatorLiskDAO $object) {
     throw new Exception('Capability not supported.');
   }
 
 
   /**
    * @task mail
    */
   protected function getMailTo(PhabricatorLiskDAO $object) {
     throw new Exception('Capability not supported.');
   }
 
 
   /**
    * @task mail
    */
   protected function getMailCC(PhabricatorLiskDAO $object) {
     $phids = array();
     $has_support = false;
 
     if ($object instanceof PhabricatorSubscribableInterface) {
       $phids[] = $this->subscribers;
       $has_support = true;
     }
 
     if ($object instanceof PhabricatorProjectInterface) {
       $project_phids = PhabricatorEdgeQuery::loadDestinationPHIDs(
         $object->getPHID(),
         PhabricatorProjectObjectHasProjectEdgeType::EDGECONST);
 
       if ($project_phids) {
         $watcher_type = PhabricatorEdgeConfig::TYPE_OBJECT_HAS_WATCHER;
 
         $query = id(new PhabricatorEdgeQuery())
           ->withSourcePHIDs($project_phids)
           ->withEdgeTypes(array($watcher_type));
         $query->execute();
 
         $watcher_phids = $query->getDestinationPHIDs();
         if ($watcher_phids) {
           // We need to do a visibility check for all the watchers, as
           // watching a project is not a guarantee that you can see objects
           // associated with it.
           $users = id(new PhabricatorPeopleQuery())
             ->setViewer($this->requireActor())
             ->withPHIDs($watcher_phids)
             ->execute();
 
           $watchers = array();
           foreach ($users as $user) {
             $can_see = PhabricatorPolicyFilter::hasCapability(
               $user,
               $object,
               PhabricatorPolicyCapability::CAN_VIEW);
             if ($can_see) {
               $watchers[] = $user->getPHID();
             }
           }
           $phids[] = $watchers;
         }
       }
 
       $has_support = true;
     }
 
     if (!$has_support) {
       throw new Exception('Capability not supported.');
     }
 
     return array_mergev($phids);
   }
 
 
   /**
    * @task mail
    */
   protected function buildMailBody(
     PhabricatorLiskDAO $object,
     array $xactions) {
 
     $headers = array();
     $comments = array();
 
     foreach ($xactions as $xaction) {
       if ($xaction->shouldHideForMail($xactions)) {
         continue;
       }
 
       $header = $xaction->getTitleForMail();
       if ($header !== null) {
         $headers[] = $header;
       }
 
       $comment = $xaction->getBodyForMail();
       if ($comment !== null) {
         $comments[] = $comment;
       }
     }
 
     $body = new PhabricatorMetaMTAMailBody();
     $body->addRawSection(implode("\n", $headers));
 
     foreach ($comments as $comment) {
       $body->addRawSection($comment);
     }
 
     if ($object instanceof PhabricatorCustomFieldInterface) {
       $field_list = PhabricatorCustomField::getObjectFields(
         $object,
         PhabricatorCustomField::ROLE_TRANSACTIONMAIL);
       $field_list->setViewer($this->getActor());
       $field_list->readFieldsFromStorage($object);
 
       foreach ($field_list->getFields() as $field) {
         $field->updateTransactionMailBody(
           $body,
           $this,
           $xactions);
       }
     }
 
     return $body;
   }
 
 
 /* -(  Publishing Feed Stories  )-------------------------------------------- */
 
 
   /**
    * @task feed
    */
   protected function shouldPublishFeedStory(
     PhabricatorLiskDAO $object,
     array $xactions) {
     return false;
   }
 
 
   /**
    * @task feed
    */
   protected function getFeedStoryType() {
     return 'PhabricatorApplicationTransactionFeedStory';
   }
 
 
   /**
    * @task feed
    */
   protected function getFeedRelatedPHIDs(
     PhabricatorLiskDAO $object,
     array $xactions) {
 
     $phids = array(
       $object->getPHID(),
       $this->getActingAsPHID(),
     );
 
     if ($object instanceof PhabricatorProjectInterface) {
       $project_phids = PhabricatorEdgeQuery::loadDestinationPHIDs(
         $object->getPHID(),
         PhabricatorProjectObjectHasProjectEdgeType::EDGECONST);
       foreach ($project_phids as $project_phid) {
         $phids[] = $project_phid;
       }
     }
 
     return $phids;
   }
 
 
   /**
    * @task feed
    */
   protected function getFeedNotifyPHIDs(
     PhabricatorLiskDAO $object,
     array $xactions) {
 
     return array_unique(array_merge(
       $this->getMailTo($object),
       $this->getMailCC($object)));
   }
 
 
   /**
    * @task feed
    */
   protected function getFeedStoryData(
     PhabricatorLiskDAO $object,
     array $xactions) {
 
     $xactions = msort($xactions, 'getActionStrength');
     $xactions = array_reverse($xactions);
 
     return array(
       'objectPHID'        => $object->getPHID(),
       'transactionPHIDs'  => mpull($xactions, 'getPHID'),
     );
   }
 
 
   /**
    * @task feed
    */
   protected function publishFeedStory(
     PhabricatorLiskDAO $object,
     array $xactions,
     array $mailed_phids) {
 
     $xactions = mfilter($xactions, 'shouldHideForFeed', true);
 
     if (!$xactions) {
       return;
     }
 
     $related_phids = $this->getFeedRelatedPHIDs($object, $xactions);
     $subscribed_phids = $this->getFeedNotifyPHIDs($object, $xactions);
 
     $story_type = $this->getFeedStoryType();
     $story_data = $this->getFeedStoryData($object, $xactions);
 
     id(new PhabricatorFeedStoryPublisher())
       ->setStoryType($story_type)
       ->setStoryData($story_data)
       ->setStoryTime(time())
       ->setStoryAuthorPHID($this->getActingAsPHID())
       ->setRelatedPHIDs($related_phids)
       ->setPrimaryObjectPHID($object->getPHID())
       ->setSubscribedPHIDs($subscribed_phids)
       ->setMailRecipientPHIDs($mailed_phids)
+      ->setMailTags($this->getMailTags($object, $xactions))
       ->publish();
   }
 
 
 /* -(  Search Index  )------------------------------------------------------- */
 
 
   /**
    * @task search
    */
   protected function supportsSearch() {
     return false;
   }
 
 
 /* -(  Herald Integration )-------------------------------------------------- */
 
 
   protected function shouldApplyHeraldRules(
     PhabricatorLiskDAO $object,
     array $xactions) {
     return false;
   }
 
   protected function buildHeraldAdapter(
     PhabricatorLiskDAO $object,
     array $xactions) {
     throw new Exception('No herald adapter specified.');
   }
 
   private function setHeraldAdapter(HeraldAdapter $adapter) {
     $this->heraldAdapter = $adapter;
     return $this;
   }
 
   protected function getHeraldAdapter() {
     return $this->heraldAdapter;
   }
 
   private function setHeraldTranscript(HeraldTranscript $transcript) {
     $this->heraldTranscript = $transcript;
     return $this;
   }
 
   protected function getHeraldTranscript() {
     return $this->heraldTranscript;
   }
 
   private function applyHeraldRules(
     PhabricatorLiskDAO $object,
     array $xactions) {
 
     $adapter = $this->buildHeraldAdapter($object, $xactions);
     $adapter->setContentSource($this->getContentSource());
     $adapter->setIsNewObject($this->getIsNewObject());
     $xscript = HeraldEngine::loadAndApplyRules($adapter);
 
     $this->setHeraldAdapter($adapter);
     $this->setHeraldTranscript($xscript);
 
     return array_merge(
       $this->didApplyHeraldRules($object, $adapter, $xscript),
       $adapter->getQueuedTransactions());
   }
 
   protected function didApplyHeraldRules(
     PhabricatorLiskDAO $object,
     HeraldAdapter $adapter,
     HeraldTranscript $transcript) {
     return array();
   }
 
 
 /* -(  Custom Fields  )------------------------------------------------------ */
 
 
   /**
    * @task customfield
    */
   private function getCustomFieldForTransaction(
     PhabricatorLiskDAO $object,
     PhabricatorApplicationTransaction $xaction) {
 
     $field_key = $xaction->getMetadataValue('customfield:key');
     if (!$field_key) {
       throw new Exception(
         "Custom field transaction has no 'customfield:key'!");
     }
 
     $field = PhabricatorCustomField::getObjectField(
       $object,
       PhabricatorCustomField::ROLE_APPLICATIONTRANSACTIONS,
       $field_key);
 
     if (!$field) {
       throw new Exception(
         "Custom field transaction has invalid 'customfield:key'; field ".
         "'{$field_key}' is disabled or does not exist.");
     }
 
     if (!$field->shouldAppearInApplicationTransactions()) {
       throw new Exception(
         "Custom field transaction '{$field_key}' does not implement ".
         "integration for ApplicationTransactions.");
     }
 
     $field->setViewer($this->getActor());
 
     return $field;
   }
 
 
 /* -(  Files  )-------------------------------------------------------------- */
 
 
   /**
    * Extract the PHIDs of any files which these transactions attach.
    *
    * @task files
    */
   private function extractFilePHIDs(
     PhabricatorLiskDAO $object,
     array $xactions) {
 
     $blocks = array();
     foreach ($xactions as $xaction) {
       $blocks[] = $this->getRemarkupBlocksFromTransaction($xaction);
     }
     $blocks = array_mergev($blocks);
 
     $phids = array();
     if ($blocks) {
       $phids[] = PhabricatorMarkupEngine::extractFilePHIDsFromEmbeddedFiles(
         $this->getActor(),
         $blocks);
     }
 
     foreach ($xactions as $xaction) {
       $phids[] = $this->extractFilePHIDsFromCustomTransaction(
         $object,
         $xaction);
     }
 
     $phids = array_unique(array_filter(array_mergev($phids)));
     if (!$phids) {
       return array();
     }
 
     // Only let a user attach files they can actually see, since this would
     // otherwise let you access any file by attaching it to an object you have
     // view permission on.
 
     $files = id(new PhabricatorFileQuery())
       ->setViewer($this->getActor())
       ->withPHIDs($phids)
       ->execute();
 
     return mpull($files, 'getPHID');
   }
 
   /**
    * @task files
    */
   protected function extractFilePHIDsFromCustomTransaction(
     PhabricatorLiskDAO $object,
     PhabricatorApplicationTransaction $xaction) {
     return array();
   }
 
 
   /**
    * @task files
    */
   private function attachFiles(
     PhabricatorLiskDAO $object,
     array $file_phids) {
 
     if (!$file_phids) {
       return;
     }
 
     $editor = new PhabricatorEdgeEditor();
 
     $src = $object->getPHID();
     $type = PhabricatorEdgeConfig::TYPE_OBJECT_HAS_FILE;
     foreach ($file_phids as $dst) {
       $editor->addEdge($src, $type, $dst);
     }
 
     $editor->save();
   }
 
   private function applyInverseEdgeTransactions(
     PhabricatorLiskDAO $object,
     PhabricatorApplicationTransaction $xaction,
     $inverse_type) {
 
     $old = $xaction->getOldValue();
     $new = $xaction->getNewValue();
 
     $add = array_keys(array_diff_key($new, $old));
     $rem = array_keys(array_diff_key($old, $new));
 
     $add = array_fuse($add);
     $rem = array_fuse($rem);
     $all = $add + $rem;
 
     $nodes = id(new PhabricatorObjectQuery())
       ->setViewer($this->requireActor())
       ->withPHIDs($all)
       ->execute();
 
     foreach ($nodes as $node) {
       if (!($node instanceof PhabricatorApplicationTransactionInterface)) {
         continue;
       }
 
       $editor = $node->getApplicationTransactionEditor();
       $template = $node->getApplicationTransactionTemplate();
       $target = $node->getApplicationTransactionObject();
 
       if (isset($add[$node->getPHID()])) {
         $edge_edit_type = '+';
       } else {
         $edge_edit_type = '-';
       }
 
       $template
         ->setTransactionType($xaction->getTransactionType())
         ->setMetadataValue('edge:type', $inverse_type)
         ->setNewValue(
           array(
             $edge_edit_type => array($object->getPHID() => $object->getPHID()),
           ));
 
       $editor
         ->setContinueOnNoEffect(true)
         ->setContinueOnMissingFields(true)
         ->setParentMessageID($this->getParentMessageID())
         ->setIsInverseEdgeEditor(true)
         ->setActor($this->requireActor())
         ->setActingAsPHID($this->getActingAsPHID())
         ->setContentSource($this->getContentSource());
 
       $editor->applyTransactions($target, array($template));
     }
   }
 
 }