diff --git a/src/applications/conpherence/mail/ConpherenceReplyHandler.php b/src/applications/conpherence/mail/ConpherenceReplyHandler.php
--- a/src/applications/conpherence/mail/ConpherenceReplyHandler.php
+++ b/src/applications/conpherence/mail/ConpherenceReplyHandler.php
@@ -20,11 +20,11 @@
 
   public function getPrivateReplyHandlerEmailAddress(
     PhabricatorObjectHandle $handle) {
-    return $this->getDefaultPrivateReplyHandlerEmailAddress($handle, 'E');
+    return $this->getDefaultPrivateReplyHandlerEmailAddress($handle, 'Z');
   }
 
   public function getPublicReplyHandlerEmailAddress() {
-    return $this->getDefaultPublicReplyHandlerEmailAddress('E');
+    return $this->getDefaultPublicReplyHandlerEmailAddress('Z');
   }
 
   public function getReplyHandlerInstructions() {
diff --git a/src/applications/conpherence/mail/ConpherenceThreadMailReceiver.php b/src/applications/conpherence/mail/ConpherenceThreadMailReceiver.php
--- a/src/applications/conpherence/mail/ConpherenceThreadMailReceiver.php
+++ b/src/applications/conpherence/mail/ConpherenceThreadMailReceiver.php
@@ -9,11 +9,13 @@
   }
 
   protected function getObjectPattern() {
-    return 'E[1-9]\d*';
+    // TODO: Only recognize "Z" once we get closer to shipping Calendar.
+    return '[EZ][1-9]\d*';
   }
 
   protected function loadObject($pattern, PhabricatorUser $viewer) {
-    $id = (int)trim($pattern, 'E');
+    // TODO: Only recognize "Z" once we get closer to shipping Calendar.
+    $id = (int)trim($pattern, 'EZ');
 
     return id(new ConpherenceThreadQuery())
       ->setViewer($viewer)