diff --git a/scripts/mail/mail_handler.php b/scripts/mail/mail_handler.php
--- a/scripts/mail/mail_handler.php
+++ b/scripts/mail/mail_handler.php
@@ -77,6 +77,7 @@
     $attachment->getContent(),
     array(
       'name' => $attachment->getFilename(),
+      'viewPolicy' => PhabricatorPolicies::POLICY_NOONE,
     ));
   $attachments[] = $file->getPHID();
 }
diff --git a/src/applications/metamta/controller/PhabricatorMetaMTAMailgunReceiveController.php b/src/applications/metamta/controller/PhabricatorMetaMTAMailgunReceiveController.php
--- a/src/applications/metamta/controller/PhabricatorMetaMTAMailgunReceiveController.php
+++ b/src/applications/metamta/controller/PhabricatorMetaMTAMailgunReceiveController.php
@@ -56,7 +56,7 @@
         $file = PhabricatorFile::newFromPHPUpload(
           $file_raw,
           array(
-            'authorPHID' => $user->getPHID(),
+            'viewPolicy' => PhabricatorPolicies::POLICY_NOONE,
           ));
         $file_phids[] = $file->getPHID();
       } catch (Exception $ex) {
diff --git a/src/applications/metamta/controller/PhabricatorMetaMTASendGridReceiveController.php b/src/applications/metamta/controller/PhabricatorMetaMTASendGridReceiveController.php
--- a/src/applications/metamta/controller/PhabricatorMetaMTASendGridReceiveController.php
+++ b/src/applications/metamta/controller/PhabricatorMetaMTASendGridReceiveController.php
@@ -42,7 +42,7 @@
         $file = PhabricatorFile::newFromPHPUpload(
           $file_raw,
           array(
-            'authorPHID' => $user->getPHID(),
+            'viewPolicy' => PhabricatorPolicies::POLICY_NOONE,
           ));
         $file_phids[] = $file->getPHID();
       } catch (Exception $ex) {
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
@@ -327,11 +327,8 @@
       return $body;
     }
 
-    // NOTE: This is safe, but not entirely correct. Clean it up after
-    // T7712. These files have the install-default policy right now, which
-    // may or may not be permissive.
     $files = id(new PhabricatorFileQuery())
-      ->setViewer(PhabricatorUser::getOmnipotentUser())
+      ->setViewer($this->getActor())
       ->withPHIDs($attachments)
       ->execute();
 
diff --git a/src/applications/metamta/storage/PhabricatorMetaMTAReceivedMail.php b/src/applications/metamta/storage/PhabricatorMetaMTAReceivedMail.php
--- a/src/applications/metamta/storage/PhabricatorMetaMTAReceivedMail.php
+++ b/src/applications/metamta/storage/PhabricatorMetaMTAReceivedMail.php
@@ -121,6 +121,19 @@
 
       $this->setAuthorPHID($sender->getPHID());
 
+      // Now that we've identified the sender, mark them as the author of
+      // any attached files.
+      $attachments = $this->getAttachments();
+      if ($attachments) {
+        $files = id(new PhabricatorFileQuery())
+          ->setViewer(PhabricatorUser::getOmnipotentUser())
+          ->withPHIDs($attachments)
+          ->execute();
+        foreach ($files as $file) {
+          $file->setAuthorPHID($sender->getPHID())->save();
+        }
+      }
+
       $receiver->receiveMail($this, $sender);
     } catch (PhabricatorMetaMTAReceivedMailProcessingException $ex) {
       switch ($ex->getStatusCode()) {