Paul Reinheimer has posted about his experiences with sending mail, specifically as it relates to using the Zend_Mail component from the Zend Framework to handle the details.

Like every product, Natural Load Testing needs to send some mail, having written and re-written a bunch of different blocks of mail code over the years, I wanted to come up with something that would work now, and continue to serve us well into the future.

He chose Zend_Mail to fulfill some of his requirements (multipart emails, sending custom emails, templates for automatic emails) and includes some sample code showing it at work. The result is an object that can be created and, by calling a "basic" method, can send an email based on an HTML template (using the HTML Email Boilerplate for the base styling).