protected function getDefaultPrivateReplyHandlerEmailAddress(PhabricatorObjectHandle $handle, $prefix)
 {
     if ($handle->getType() != PhabricatorPHIDConstants::PHID_TYPE_USER) {
         // You must be a real user to get a private reply handler address.
         return null;
     }
     $receiver = $this->getMailReceiver();
     $receiver_id = $receiver->getID();
     $user_id = $handle->getAlternateID();
     $hash = PhabricatorMetaMTAReceivedMail::computeMailHash($receiver->getMailKey(), $handle->getPHID());
     $domain = $this->getReplyHandlerDomain();
     $address = "{$prefix}{$receiver_id}+{$user_id}+{$hash}@{$domain}";
     return $this->getSingleReplyHandlerPrefix($address);
 }