Cal Evans has written up an article for php|architect's ART (article repository) covering "Zen(d) and the Art of Email", a look at the use of the Zend_Mail package from the Zend Framwork.
Since the beginning of Internet time man has strived for the best way to send emails from a program. Whether a web page that notifies its owner when an order is placed to merchants sending a welcomed message to its closest 250,000 customers; man continues to strive for the best way to communicate without having to be personal. With the advent of the Zend Framework, we have another weapon in the arsenal, Zend_Mail.
He talks briefly about advantages that the Zend_Mail package has over the traditional mail() and starts off with some sample code to illustrate it's abilities right off. The rest of the tutorial is used to explain this example, breaking it down chunk by chunk - all the way down to sending the closing statements to the remote mail server.