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SMTP Authentication - Zend_Mail
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.
Example #1 Enabling authentication within Zend_Mail_Transport_Smtp
Note: 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.