setLocalDomain() public method

This should be a fully-qualified domain name and should be truly the domain you're using. If your server doesn't have a domain name, use the IP in square brackets (i.e. [127.0.0.1]).
public setLocalDomain ( string $domain ) : Swift_Transport_AbstractSmtpTransport
$domain string
return Swift_Transport_AbstractSmtpTransport
 /**
  * Sets the local domain based on the current request context.
  */
 public function configure(\Swift_Transport_AbstractSmtpTransport $transport)
 {
     if ($this->localDomain) {
         $transport->setLocalDomain($this->localDomain);
     } elseif ($this->requestContext) {
         $transport->setLocalDomain($this->requestContext->getHost());
     }
 }