diff --git a/src/applications/conpherence/editor/ConpherenceEditor.php b/src/applications/conpherence/editor/ConpherenceEditor.php
--- a/src/applications/conpherence/editor/ConpherenceEditor.php
+++ b/src/applications/conpherence/editor/ConpherenceEditor.php
@@ -497,8 +497,8 @@
     $phid = $object->getPHID();
 
     return id(new PhabricatorMetaMTAMail())
-      ->setSubject("E{$id}: {$title}")
-      ->addHeader('Thread-Topic', "E{$id}: {$phid}");
+      ->setSubject("Z{$id}: {$title}")
+      ->addHeader('Thread-Topic', "Z{$id}: {$phid}");
   }
 
   protected function getMailTo(PhabricatorLiskDAO $object) {
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
@@ -9,13 +9,11 @@
   }
 
   protected function getObjectPattern() {
-    // TODO: Only recognize "Z" once we get closer to shipping Calendar.
-    return '[EZ][1-9]\d*';
+    return 'Z[1-9]\d*';
   }
 
   protected function loadObject($pattern, PhabricatorUser $viewer) {
-    // TODO: Only recognize "Z" once we get closer to shipping Calendar.
-    $id = (int)trim($pattern, 'EZ');
+    $id = (int)trim($pattern, 'Z');
 
     return id(new ConpherenceThreadQuery())
       ->setViewer($viewer)