diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -2220,6 +2220,7 @@
     'PhabricatorBoardResponseEngine' => 'applications/project/engine/PhabricatorBoardResponseEngine.php',
     'PhabricatorBoolConfigType' => 'applications/config/type/PhabricatorBoolConfigType.php',
     'PhabricatorBoolEditField' => 'applications/transactions/editfield/PhabricatorBoolEditField.php',
+    'PhabricatorBoolMailStamp' => 'applications/metamta/stamp/PhabricatorBoolMailStamp.php',
     'PhabricatorBritishEnglishTranslation' => 'infrastructure/internationalization/translation/PhabricatorBritishEnglishTranslation.php',
     'PhabricatorBuiltinDraftEngine' => 'applications/transactions/draft/PhabricatorBuiltinDraftEngine.php',
     'PhabricatorBuiltinFileCachePurger' => 'applications/cache/purger/PhabricatorBuiltinFileCachePurger.php',
@@ -2813,6 +2814,7 @@
     'PhabricatorEditPage' => 'applications/transactions/editengine/PhabricatorEditPage.php',
     'PhabricatorEditType' => 'applications/transactions/edittype/PhabricatorEditType.php',
     'PhabricatorEditor' => 'infrastructure/PhabricatorEditor.php',
+    'PhabricatorEditorMailEngineExtension' => 'applications/transactions/engineextension/PhabricatorEditorMailEngineExtension.php',
     'PhabricatorEditorMultipleSetting' => 'applications/settings/setting/PhabricatorEditorMultipleSetting.php',
     'PhabricatorEditorSetting' => 'applications/settings/setting/PhabricatorEditorSetting.php',
     'PhabricatorElasticFulltextStorageEngine' => 'applications/search/fulltextstorage/PhabricatorElasticFulltextStorageEngine.php',
@@ -3440,6 +3442,7 @@
     'PhabricatorPHIDListEditField' => 'applications/transactions/editfield/PhabricatorPHIDListEditField.php',
     'PhabricatorPHIDListEditType' => 'applications/transactions/edittype/PhabricatorPHIDListEditType.php',
     'PhabricatorPHIDListExportField' => 'infrastructure/export/field/PhabricatorPHIDListExportField.php',
+    'PhabricatorPHIDMailStamp' => 'applications/metamta/stamp/PhabricatorPHIDMailStamp.php',
     'PhabricatorPHIDResolver' => 'applications/phid/resolver/PhabricatorPHIDResolver.php',
     'PhabricatorPHIDType' => 'applications/phid/type/PhabricatorPHIDType.php',
     'PhabricatorPHIDTypeTestCase' => 'applications/phid/type/__tests__/PhabricatorPHIDTypeTestCase.php',
@@ -4395,6 +4398,7 @@
     'PhabricatorVersionedDraft' => 'applications/draft/storage/PhabricatorVersionedDraft.php',
     'PhabricatorVeryWowEnglishTranslation' => 'infrastructure/internationalization/translation/PhabricatorVeryWowEnglishTranslation.php',
     'PhabricatorViewerDatasource' => 'applications/people/typeahead/PhabricatorViewerDatasource.php',
+    'PhabricatorViewerMailStamp' => 'applications/metamta/stamp/PhabricatorViewerMailStamp.php',
     'PhabricatorWatcherHasObjectEdgeType' => 'applications/transactions/edges/PhabricatorWatcherHasObjectEdgeType.php',
     'PhabricatorWebContentSource' => 'infrastructure/contentsource/PhabricatorWebContentSource.php',
     'PhabricatorWebServerSetupCheck' => 'applications/config/check/PhabricatorWebServerSetupCheck.php',
@@ -7582,6 +7586,7 @@
     'PhabricatorBoardResponseEngine' => 'Phobject',
     'PhabricatorBoolConfigType' => 'PhabricatorTextConfigType',
     'PhabricatorBoolEditField' => 'PhabricatorEditField',
+    'PhabricatorBoolMailStamp' => 'PhabricatorMailStamp',
     'PhabricatorBritishEnglishTranslation' => 'PhutilTranslation',
     'PhabricatorBuiltinDraftEngine' => 'PhabricatorDraftEngine',
     'PhabricatorBuiltinFileCachePurger' => 'PhabricatorCachePurger',
@@ -8267,6 +8272,7 @@
     'PhabricatorEditPage' => 'Phobject',
     'PhabricatorEditType' => 'Phobject',
     'PhabricatorEditor' => 'Phobject',
+    'PhabricatorEditorMailEngineExtension' => 'PhabricatorMailEngineExtension',
     'PhabricatorEditorMultipleSetting' => 'PhabricatorSelectSetting',
     'PhabricatorEditorSetting' => 'PhabricatorStringSetting',
     'PhabricatorElasticFulltextStorageEngine' => 'PhabricatorFulltextStorageEngine',
@@ -8973,6 +8979,7 @@
     'PhabricatorPHIDListEditField' => 'PhabricatorEditField',
     'PhabricatorPHIDListEditType' => 'PhabricatorEditType',
     'PhabricatorPHIDListExportField' => 'PhabricatorListExportField',
+    'PhabricatorPHIDMailStamp' => 'PhabricatorMailStamp',
     'PhabricatorPHIDResolver' => 'Phobject',
     'PhabricatorPHIDType' => 'Phobject',
     'PhabricatorPHIDTypeTestCase' => 'PhutilTestCase',
@@ -10137,6 +10144,7 @@
     'PhabricatorVersionedDraft' => 'PhabricatorDraftDAO',
     'PhabricatorVeryWowEnglishTranslation' => 'PhutilTranslation',
     'PhabricatorViewerDatasource' => 'PhabricatorTypeaheadDatasource',
+    'PhabricatorViewerMailStamp' => 'PhabricatorMailStamp',
     'PhabricatorWatcherHasObjectEdgeType' => 'PhabricatorEdgeType',
     'PhabricatorWebContentSource' => 'PhabricatorContentSource',
     'PhabricatorWebServerSetupCheck' => 'PhabricatorSetupCheck',
diff --git a/src/applications/metamta/stamp/PhabricatorBoolMailStamp.php b/src/applications/metamta/stamp/PhabricatorBoolMailStamp.php
new file mode 100644
--- /dev/null
+++ b/src/applications/metamta/stamp/PhabricatorBoolMailStamp.php
@@ -0,0 +1,16 @@
+<?php
+
+final class PhabricatorBoolMailStamp
+  extends PhabricatorMailStamp {
+
+  const STAMPTYPE = 'bool';
+
+  public function renderStamps($value) {
+    if (!$value) {
+      return null;
+    }
+
+    return $this->renderStamp($this->getKey());
+  }
+
+}
diff --git a/src/applications/metamta/stamp/PhabricatorPHIDMailStamp.php b/src/applications/metamta/stamp/PhabricatorPHIDMailStamp.php
new file mode 100644
--- /dev/null
+++ b/src/applications/metamta/stamp/PhabricatorPHIDMailStamp.php
@@ -0,0 +1,36 @@
+<?php
+
+final class PhabricatorPHIDMailStamp
+  extends PhabricatorMailStamp {
+
+  const STAMPTYPE = 'phid';
+
+  public function renderStamps($value) {
+    if ($value === null) {
+      return null;
+    }
+
+    $value = (array)$value;
+    if (!$value) {
+      return null;
+    }
+
+    $viewer = $this->getViewer();
+    $handles = $viewer->loadHandles($value);
+
+    $results = array();
+    foreach ($value as $phid) {
+      $handle = $handles[$phid];
+
+      $mail_name = $handle->getMailStampName();
+      if ($mail_name === null) {
+        $mail_name = $handle->getPHID();
+      }
+
+      $results[] = $this->renderStamp($this->getKey(), $mail_name);
+    }
+
+    return $results;
+  }
+
+}
diff --git a/src/applications/metamta/stamp/PhabricatorViewerMailStamp.php b/src/applications/metamta/stamp/PhabricatorViewerMailStamp.php
new file mode 100644
--- /dev/null
+++ b/src/applications/metamta/stamp/PhabricatorViewerMailStamp.php
@@ -0,0 +1,35 @@
+<?php
+
+final class PhabricatorViewerMailStamp
+  extends PhabricatorMailStamp {
+
+  const STAMPTYPE = 'viewer';
+
+  public function renderStamps($value) {
+    // If we're sending one mail to everyone, we never include viewer-based
+    // stamps since they'll only be accurate for one recipient. Recipients
+    // can still use the corresponding stamps with their usernames or PHIDs.
+    if (!PhabricatorMetaMTAMail::shouldMailEachRecipient()) {
+      return null;
+    }
+
+    $viewer_phid = $this->getViewer()->getPHID();
+    if (!$viewer_phid) {
+      return null;
+    }
+
+    if (!$value) {
+      return null;
+    }
+
+    $value = (array)$value;
+    $value = array_fuse($value);
+
+    if (!isset($value[$viewer_phid])) {
+      return null;
+    }
+
+    return $this->renderStamp($this->getKey());
+  }
+
+}
diff --git a/src/applications/people/phid/PhabricatorPeopleUserPHIDType.php b/src/applications/people/phid/PhabricatorPeopleUserPHIDType.php
--- a/src/applications/people/phid/PhabricatorPeopleUserPHIDType.php
+++ b/src/applications/people/phid/PhabricatorPeopleUserPHIDType.php
@@ -39,11 +39,14 @@
     foreach ($handles as $phid => $handle) {
       $user = $objects[$phid];
       $realname = $user->getRealName();
-
-      $handle->setName($user->getUsername());
-      $handle->setURI('/p/'.$user->getUsername().'/');
-      $handle->setFullName($user->getFullName());
-      $handle->setImageURI($user->getProfileImageURI());
+      $username = $user->getUsername();
+
+      $handle
+        ->setName($username)
+        ->setURI('/p/'.$username.'/')
+        ->setFullName($user->getFullName())
+        ->setImageURI($user->getProfileImageURI())
+        ->setMailStampName('@'.$username);
 
       if ($user->getIsMailingList()) {
         $handle->setIcon('fa-envelope-o');
diff --git a/src/applications/phid/PhabricatorObjectHandle.php b/src/applications/phid/PhabricatorObjectHandle.php
--- a/src/applications/phid/PhabricatorObjectHandle.php
+++ b/src/applications/phid/PhabricatorObjectHandle.php
@@ -31,6 +31,7 @@
   private $subtitle;
   private $tokenIcon;
   private $commandLineObjectName;
+  private $mailStampName;
 
   private $stateIcon;
   private $stateColor;
@@ -134,6 +135,15 @@
     return $this->objectName;
   }
 
+  public function setMailStampName($mail_stamp_name) {
+    $this->mailStampName = $mail_stamp_name;
+    return $this;
+  }
+
+  public function getMailStampName() {
+    return $this->mailStampName;
+  }
+
   public function setURI($uri) {
     $this->uri = $uri;
     return $this;
diff --git a/src/applications/project/phid/PhabricatorProjectProjectPHIDType.php b/src/applications/project/phid/PhabricatorProjectProjectPHIDType.php
--- a/src/applications/project/phid/PhabricatorProjectProjectPHIDType.php
+++ b/src/applications/project/phid/PhabricatorProjectProjectPHIDType.php
@@ -45,11 +45,12 @@
 
       if (strlen($slug)) {
         $handle->setObjectName('#'.$slug);
+        $handle->setMailStampName('#'.$slug);
         $handle->setURI("/tag/{$slug}/");
       } else {
         // We set the name to the project's PHID to avoid a parse error when a
         // project has no hashtag (as is the case with milestones by default).
-        // See T12659 for more details
+        // See T12659 for more details.
         $handle->setCommandLineObjectName($project->getPHID());
         $handle->setURI("/project/view/{$id}/");
       }
diff --git a/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php b/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php
--- a/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php
+++ b/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php
@@ -179,7 +179,7 @@
     return $this->isNewObject;
   }
 
-  protected function getMentionedPHIDs() {
+  public function getMentionedPHIDs() {
     return $this->mentionedPHIDs;
   }
 
@@ -201,6 +201,10 @@
     return $this->silent;
   }
 
+  public function getMustEncrypt() {
+    return $this->mustEncrypt;
+  }
+
   public function setIsInverseEdgeEditor($is_inverse_edge_editor) {
     $this->isInverseEdgeEditor = $is_inverse_edge_editor;
     return $this;
diff --git a/src/applications/transactions/engineextension/PhabricatorEditorMailEngineExtension.php b/src/applications/transactions/engineextension/PhabricatorEditorMailEngineExtension.php
new file mode 100644
--- /dev/null
+++ b/src/applications/transactions/engineextension/PhabricatorEditorMailEngineExtension.php
@@ -0,0 +1,81 @@
+<?php
+
+final class PhabricatorEditorMailEngineExtension
+  extends PhabricatorMailEngineExtension {
+
+  const EXTENSIONKEY = 'editor';
+
+  public function supportsObject($object) {
+    return true;
+  }
+
+  public function newMailStampTemplates($object) {
+    $templates = array();
+
+    $templates[] = id(new PhabricatorPHIDMailStamp())
+      ->setKey('actor')
+      ->setLabel(pht('Acting User'));
+
+    $templates[] = id(new PhabricatorStringMailStamp())
+      ->setKey('via')
+      ->setLabel(pht('Via Content Source'));
+
+    $templates[] = id(new PhabricatorBoolMailStamp())
+      ->setKey('silent')
+      ->setLabel(pht('Silent Edit'));
+
+    $templates[] = id(new PhabricatorBoolMailStamp())
+      ->setKey('encrypted')
+      ->setLabel(pht('Encryption Required'));
+
+    $templates[] = id(new PhabricatorBoolMailStamp())
+      ->setKey('new')
+      ->setLabel(pht('New Object'));
+
+    $templates[] = id(new PhabricatorPHIDMailStamp())
+      ->setKey('mention')
+      ->setLabel(pht('Mentioned User'));
+
+    $templates[] = id(new PhabricatorViewerMailStamp())
+      ->setKey('self-actor')
+      ->setLabel(pht('You Acted'));
+
+    $templates[] = id(new PhabricatorViewerMailStamp())
+      ->setKey('self-mention')
+      ->setLabel(pht('You Were Mentioned'));
+
+    return $templates;
+  }
+
+  public function newMailStamps($object, array $xactions) {
+    $editor = $this->getEditor();
+    $viewer = $this->getViewer();
+
+    $this->getMailStamp('actor')
+      ->setValue($editor->getActingAsPHID());
+
+    $content_source = $editor->getContentSource();
+    $this->getMailStamp('via')
+      ->setValue($content_source->getSourceTypeConstant());
+
+    $this->getMailStamp('silent')
+      ->setValue($editor->getIsSilent());
+
+    $this->getMailStamp('encrypted')
+      ->setValue($editor->getMustEncrypt());
+
+    $this->getMailStamp('new')
+      ->setValue($editor->getIsNewObject());
+
+    $mentioned_phids = $editor->getMentionedPHIDs();
+    $this->getMailStamp('mention')
+      ->setValue($mentioned_phids);
+
+    $this->getMailStamp('self-actor')
+      ->setValue($editor->getActingAsPHID());
+
+    $this->getMailStamp('self-mention')
+      ->setValue($mentioned_phids);
+  }
+
+}