diff --git a/src/applications/audit/editor/PhabricatorAuditEditor.php b/src/applications/audit/editor/PhabricatorAuditEditor.php
--- a/src/applications/audit/editor/PhabricatorAuditEditor.php
+++ b/src/applications/audit/editor/PhabricatorAuditEditor.php
@@ -496,7 +496,6 @@
       $phids[] = $object->getAuthorPHID();
     }
 
-    $status_resigned = PhabricatorAuditStatusConstants::RESIGNED;
     foreach ($object->getAudits() as $audit) {
       if (!$audit->isInteresting()) {
         // Don't send mail to uninteresting auditors, like packages which
@@ -504,7 +503,7 @@
         continue;
       }
 
-      if ($audit->getAuditStatus() != $status_resigned) {
+      if (!$audit->isResigned()) {
         $phids[] = $audit->getAuditorPHID();
       }
     }
@@ -514,6 +513,18 @@
     return $phids;
   }
 
+  protected function newMailUnexpandablePHIDs(PhabricatorLiskDAO $object) {
+    $phids = array();
+
+    foreach ($object->getAudits() as $auditor) {
+      if ($auditor->isResigned()) {
+        $phids[] = $auditor->getAuditorPHID();
+      }
+    }
+
+    return $phids;
+  }
+
   protected function buildMailBody(
     PhabricatorLiskDAO $object,
     array $xactions) {
diff --git a/src/applications/differential/editor/DifferentialTransactionEditor.php b/src/applications/differential/editor/DifferentialTransactionEditor.php
--- a/src/applications/differential/editor/DifferentialTransactionEditor.php
+++ b/src/applications/differential/editor/DifferentialTransactionEditor.php
@@ -644,6 +644,18 @@
     return $phids;
   }
 
+  protected function newMailUnexpandablePHIDs(PhabricatorLiskDAO $object) {
+    $phids = array();
+
+    foreach ($object->getReviewers() as $reviewer) {
+      if ($reviewer->isResigned()) {
+        $phids[] = $reviewer->getReviewerPHID();
+      }
+    }
+
+    return $phids;
+  }
+
   protected function getMailAction(
     PhabricatorLiskDAO $object,
     array $xactions) {
diff --git a/src/applications/differential/storage/DifferentialRevision.php b/src/applications/differential/storage/DifferentialRevision.php
--- a/src/applications/differential/storage/DifferentialRevision.php
+++ b/src/applications/differential/storage/DifferentialRevision.php
@@ -820,9 +820,15 @@
     }
 
     foreach ($reviewers as $reviewer) {
-      if ($reviewer->getReviewerPHID() == $phid) {
-        return true;
+      if ($reviewer->getReviewerPHID() !== $phid) {
+        continue;
       }
+
+      if ($reviewer->isResigned()) {
+        continue;
+      }
+
+      return true;
     }
 
     return false;
diff --git a/src/applications/metamta/replyhandler/PhabricatorMailReplyHandler.php b/src/applications/metamta/replyhandler/PhabricatorMailReplyHandler.php
--- a/src/applications/metamta/replyhandler/PhabricatorMailReplyHandler.php
+++ b/src/applications/metamta/replyhandler/PhabricatorMailReplyHandler.php
@@ -6,6 +6,7 @@
   private $applicationEmail;
   private $actor;
   private $excludePHIDs = array();
+  private $unexpandablePHIDs = array();
 
   final public function setMailReceiver($mail_receiver) {
     $this->validateMailReceiver($mail_receiver);
@@ -45,6 +46,15 @@
     return $this->excludePHIDs;
   }
 
+  public function setUnexpandablePHIDs(array $phids) {
+    $this->unexpandablePHIDs = $phids;
+    return $this;
+  }
+
+  public function getUnexpandablePHIDs() {
+    return $this->unexpandablePHIDs;
+  }
+
   abstract public function validateMailReceiver($mail_receiver);
   abstract public function getPrivateReplyHandlerEmailAddress(
     PhabricatorUser $user);
@@ -297,6 +307,16 @@
     $to_result = array();
     $cc_result = array();
 
+    // "Unexpandable" users have disengaged from an object (for example,
+    // by resigning from a revision).
+
+    // If such a user is still a direct recipient (for example, they're still
+    // on the Subscribers list) they're fair game, but group targets (like
+    // projects) will no longer include them when expanded.
+
+    $unexpandable = $this->getUnexpandablePHIDs();
+    $unexpandable = array_fuse($unexpandable);
+
     $all_phids = array_merge($to, $cc);
     if ($all_phids) {
       $map = id(new PhabricatorMetaMTAMemberQuery())
@@ -305,11 +325,21 @@
         ->execute();
       foreach ($to as $phid) {
         foreach ($map[$phid] as $expanded) {
+          if ($expanded !== $phid) {
+            if (isset($unexpandable[$expanded])) {
+              continue;
+            }
+          }
           $to_result[$expanded] = $expanded;
         }
       }
       foreach ($cc as $phid) {
         foreach ($map[$phid] as $expanded) {
+          if ($expanded !== $phid) {
+            if (isset($unexpandable[$expanded])) {
+              continue;
+            }
+          }
           $cc_result[$expanded] = $expanded;
         }
       }
diff --git a/src/applications/repository/storage/PhabricatorRepositoryAuditRequest.php b/src/applications/repository/storage/PhabricatorRepositoryAuditRequest.php
--- a/src/applications/repository/storage/PhabricatorRepositoryAuditRequest.php
+++ b/src/applications/repository/storage/PhabricatorRepositoryAuditRequest.php
@@ -72,6 +72,15 @@
     return true;
   }
 
+  public function isResigned() {
+    switch ($this->getAuditStatus()) {
+      case PhabricatorAuditStatusConstants::RESIGNED:
+        return true;
+    }
+
+    return false;
+  }
+
 
 /* -(  PhabricatorPolicyInterface  )----------------------------------------- */
 
diff --git a/src/applications/repository/storage/PhabricatorRepositoryCommit.php b/src/applications/repository/storage/PhabricatorRepositoryCommit.php
--- a/src/applications/repository/storage/PhabricatorRepositoryCommit.php
+++ b/src/applications/repository/storage/PhabricatorRepositoryCommit.php
@@ -657,7 +657,8 @@
   public function isAutomaticallySubscribed($phid) {
 
     // TODO: This should also list auditors, but handling that is a bit messy
-    // right now because we are not guaranteed to have the data.
+    // right now because we are not guaranteed to have the data. (It should not
+    // include resigned auditors.)
 
     return ($phid == $this->getAuthorPHID());
   }
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
@@ -77,6 +77,7 @@
   private $oldTo = array();
   private $oldCC = array();
   private $mailRemovedPHIDs = array();
+  private $mailUnexpandablePHIDs = array();
 
   private $transactionQueue = array();
 
@@ -1204,6 +1205,7 @@
         $this->mailShouldSend = true;
         $this->mailToPHIDs = $this->getMailTo($object);
         $this->mailCCPHIDs = $this->getMailCC($object);
+        $this->mailUnexpandablePHIDs = $this->newMailUnexpandablePHIDs($object);
 
         // Add any recipients who were previously on the notification list
         // but were removed by this change.
@@ -2562,7 +2564,13 @@
     $email_cc = $this->mailCCPHIDs;
     $email_cc = array_merge($email_cc, $this->heraldEmailPHIDs);
 
+    $unexpandable = $this->mailUnexpandablePHIDs;
+    if (!is_array($unexpandable)) {
+      $unexpandable = array();
+    }
+
     $targets = $this->buildReplyHandler($object)
+      ->setUnexpandablePHIDs($unexpandable)
       ->getMailTargets($email_to, $email_cc);
 
     // Set this explicitly before we start swapping out the effective actor.
@@ -2817,6 +2825,11 @@
   }
 
 
+  protected function newMailUnexpandablePHIDs(PhabricatorLiskDAO $object) {
+    return array();
+  }
+
+
   /**
    * @task mail
    */
@@ -3617,6 +3630,7 @@
       'mailShouldSend',
       'mustEncrypt',
       'mailStamps',
+      'mailUnexpandablePHIDs',
     );
   }