SwiftMailer может отправлять E-Mail с помощью внешних серверов.
вот пример, который показывает, как использовать сервер Gmail:
require_once "lib/Swift.php";
require_once "lib/Swift/Connection/SMTP.php";
//Connect to localhost on port 25
$swift =& new Swift(new Swift_Connection_SMTP("localhost"));
//Connect to an IP address on a non-standard port
$swift =& new Swift(new Swift_Connection_SMTP("217.147.94.117", 419));
//Connect to Gmail (PHP5)
$swift = new Swift(new Swift_Connection_SMTP(
"smtp.gmail.com", Swift_Connection_SMTP::PORT_SECURE, Swift_Connection_SMTP::ENC_TLS));