Swiftmailer, free feature-rich PHP mailer

 Swift Mailer is component based mailing solution for PHP
 Send emails using SMTP, sendmail, postfix or a custom Transport
 implementation of your own. It Supports servers that require username
 and password and/or encryption.
 .
 Features:
  - SMTP authentication
  - event-driven plugins to customize the library
  - MIME compliant HTML/multipart emails
  - large attachments and inline/embedded images with low memory use