Index: resources/sql/autopatches/20140106.macromailkey.1.sql
===================================================================
--- /dev/null
+++ resources/sql/autopatches/20140106.macromailkey.1.sql
@@ -0,0 +1,2 @@
+ALTER TABLE {$NAMESPACE}_file.file_imagemacro
+  ADD mailKey VARCHAR(20) NOT NULL COLLATE utf8_bin;
Index: resources/sql/autopatches/20140106.macromailkey.2.php
===================================================================
--- /dev/null
+++ resources/sql/autopatches/20140106.macromailkey.2.php
@@ -0,0 +1,23 @@
+<?php
+
+echo "Adding mailkeys to macros.\n";
+
+$table = new PhabricatorFileImageMacro();
+$conn_w = $table->establishConnection('w');
+$iterator = new LiskMigrationIterator($table);
+foreach ($iterator as $macro) {
+  $id = $macro->getID();
+
+  echo "Populating macro {$id}...\n";
+
+  if (!$macro->getMailKey()) {
+    queryfx(
+      $conn_w,
+      'UPDATE %T SET mailKey = %s WHERE id = %d',
+      $table->getTableName(),
+      Filesystem::readRandomCharacters(20),
+      $id);
+  }
+}
+
+echo "Done.\n";
Index: src/applications/macro/storage/PhabricatorFileImageMacro.php
===================================================================
--- src/applications/macro/storage/PhabricatorFileImageMacro.php
+++ src/applications/macro/storage/PhabricatorFileImageMacro.php
@@ -13,6 +13,7 @@
   protected $isDisabled = 0;
   protected $audioPHID;
   protected $audioBehavior = self::AUDIO_BEHAVIOR_NONE;
+  protected $mailKey;
 
   private $file = self::ATTACHABLE;
   private $audio = self::ATTACHABLE;
@@ -50,10 +51,18 @@
       PhabricatorMacroPHIDTypeMacro::TYPECONST);
   }
 
-  public function isAutomaticallySubscribed($phid) {
-    return false;
+
+  public function save() {
+    if (!$this->getMailKey()) {
+      $this->setMailKey(Filesystem::readRandomCharacters(20));
+    }
+    return parent::save();
   }
 
+
+/* -(  PhabricatorApplicationTransactionInterface  )------------------------- */
+
+
   public function getApplicationTransactionEditor() {
     return new PhabricatorMacroEditor();
   }
@@ -62,6 +71,18 @@
     return new PhabricatorMacroTransaction();
   }
 
+
+/* -(  PhabricatorSubscribableInterface  )----------------------------------- */
+
+
+  public function isAutomaticallySubscribed($phid) {
+    return false;
+  }
+
+
+/* -(  PhabricatorPolicyInterface  )----------------------------------------- */
+
+
   public function getCapabilities() {
     return array(
       PhabricatorPolicyCapability::CAN_VIEW,