In a pointer from RootPrompt.org today, there's this tutorial from PHPFreaks.com discussing how to send just about any kind of mail from PHP (with the help of the PHPMailer library).

Sending E-Mail through PHP can be simple, or it can be very complex depending on what you want to do. A standard plain-text E-Mail is what most developers resort to because building the MIME headers for HTML mail can be a difficult process. Those days have been over for quite some time with the amazing PHPMailer library that is available for free! In this tutorial, I will discuss in detail the features and possibilities you have when dealing with PHPMailer.

They show you the install, creating and extending a mailing class (with sample code), adding more header information (Reply-To, CC, BCC, etc) - all with good explainations for each step of the way. PHPMailer even lets you easily send emails with attachments and create mailing lists...