diff --git a/src/applications/phriction/editor/PhrictionTransactionEditor.php b/src/applications/phriction/editor/PhrictionTransactionEditor.php
--- a/src/applications/phriction/editor/PhrictionTransactionEditor.php
+++ b/src/applications/phriction/editor/PhrictionTransactionEditor.php
@@ -391,6 +391,10 @@
         pht("A document's content changes."),
       PhrictionTransaction::MAILTAG_DELETE =>
         pht('A document is deleted.'),
+      PhrictionTransaction::MAILTAG_SUBSCRIBERS =>
+        pht('A document\'s subscribers change.'),
+      PhrictionTransaction::MAILTAG_OTHER =>
+        pht('Other document activity not listed above occurs.'),
     );
   }
 
diff --git a/src/applications/phriction/storage/PhrictionTransaction.php b/src/applications/phriction/storage/PhrictionTransaction.php
--- a/src/applications/phriction/storage/PhrictionTransaction.php
+++ b/src/applications/phriction/storage/PhrictionTransaction.php
@@ -9,9 +9,11 @@
   const TYPE_MOVE_TO = 'move-to';
   const TYPE_MOVE_AWAY = 'move-away';
 
-  const MAILTAG_TITLE = 'phriction-title';
-  const MAILTAG_CONTENT = 'phriction-content';
-  const MAILTAG_DELETE  = 'phriction-delete';
+  const MAILTAG_TITLE       = 'phriction-title';
+  const MAILTAG_CONTENT     = 'phriction-content';
+  const MAILTAG_DELETE      = 'phriction-delete';
+  const MAILTAG_SUBSCRIBERS = 'phriction-subscribers';
+  const MAILTAG_OTHER       = 'phriction-other';
 
   public function getApplicationName() {
     return 'phriction';
@@ -280,7 +282,12 @@
       case self::TYPE_DELETE:
         $tags[] = self::MAILTAG_DELETE;
         break;
-
+      case PhabricatorTransactions::TYPE_SUBSCRIBERS:
+        $tags[] = self::MAILTAG_SUBSCRIBERS;
+        break;
+      default:
+        $tags[] = self::MAILTAG_OTHER;
+        break;
     }
     return $tags;
   }
diff --git a/src/applications/project/editor/PhabricatorProjectTransactionEditor.php b/src/applications/project/editor/PhabricatorProjectTransactionEditor.php
--- a/src/applications/project/editor/PhabricatorProjectTransactionEditor.php
+++ b/src/applications/project/editor/PhabricatorProjectTransactionEditor.php
@@ -433,6 +433,8 @@
         pht('Project membership changes.'),
       PhabricatorProjectTransaction::MAILTAG_WATCHERS =>
         pht('Project watcher list changes.'),
+      PhabricatorProjectTransaction::MAILTAG_SUBSCRIBERS =>
+        pht('Project subscribers change.'),
       PhabricatorProjectTransaction::MAILTAG_OTHER =>
         pht('Other project activity not listed above occurs.'),
     );
diff --git a/src/applications/project/storage/PhabricatorProjectTransaction.php b/src/applications/project/storage/PhabricatorProjectTransaction.php
--- a/src/applications/project/storage/PhabricatorProjectTransaction.php
+++ b/src/applications/project/storage/PhabricatorProjectTransaction.php
@@ -14,10 +14,11 @@
   // NOTE: This is deprecated, members are just a normal edge now.
   const TYPE_MEMBERS    = 'project:members';
 
-  const MAILTAG_METADATA = 'project-metadata';
-  const MAILTAG_MEMBERS  = 'project-members';
-  const MAILTAG_WATCHERS = 'project-watchers';
-  const MAILTAG_OTHER    = 'project-other';
+  const MAILTAG_METADATA    = 'project-metadata';
+  const MAILTAG_MEMBERS     = 'project-members';
+  const MAILTAG_SUBSCRIBERS = 'project-subscribers';
+  const MAILTAG_WATCHERS    = 'project-watchers';
+  const MAILTAG_OTHER       = 'project-other';
 
   public function getApplicationName() {
     return 'project';
@@ -369,6 +370,9 @@
       case self::TYPE_COLOR:
         $tags[] = self::MAILTAG_METADATA;
         break;
+      case PhabricatorTransactions::TYPE_SUBSCRIBERS:
+        $tags[] = self::MAILTAG_SUBSCRIBERS;
+        break;
       case PhabricatorTransactions::TYPE_EDGE:
         $type = $this->getMetadata('edge:type');
         $type = head($type);