SMTP Authentication Zend_Mail supports the use of SMTP authentication, which can be enabled be passing the 'auth' parameter to the configuration array in the Zend_Mail_Transport_Smtp constructor. The available built-in authentication methods are PLAIN, LOGIN and CRAM-MD5 which all expect a 'username' and 'password' value in the configuration array. Enabling authentication within Zend_Mail_Transport_Smtp 'login', 'username' => 'myusername', 'password' => 'password'); $transport = new Zend_Mail_Transport_Smtp('mail.server.com', $config); $mail = new Zend_Mail(); $mail->setBodyText('This is the text of the mail.'); $mail->setFrom('sender@test.com', 'Some Sender'); $mail->addTo('recipient@test.com', 'Some Recipient'); $mail->setSubject('TestSubject'); $mail->send($transport); ]]> Authentication types The authentication type is case-insensitive but has no punctuation. E.g. to use CRAM-MD5 you would pass 'auth' => 'crammd5' in the Zend_Mail_Transport_Smtp constructor.