public function loadSender(PhabricatorMetaMTAReceivedMail $mail)
 {
     try {
         // Try to load the sender normally.
         return parent::loadSender($mail);
     } catch (PhabricatorMetaMTAReceivedMailProcessingException $ex) {
         // If we failed to load the sender normally, use this special legacy
         // black magic.
         // TODO: Deprecate and remove this.
         $default_author_key = 'metamta.maniphest.default-public-author';
         $default_author = PhabricatorEnv::getEnvConfig($default_author_key);
         if (!strlen($default_author)) {
             throw $ex;
         }
         $user = id(new PhabricatorUser())->loadOneWhere('username = %s', $default_author);
         if ($user) {
             return $user;
         }
         throw new PhabricatorMetaMTAReceivedMailProcessingException(MetaMTAReceivedMailStatus::STATUS_UNKNOWN_SENDER, pht("Phabricator is misconfigured, the configuration key " . "'metamta.maniphest.default-public-author' is set to user " . "'%s' but that user does not exist.", $default_author));
     }
 }