On the Techfounder blog (from Eran Galperin) there's a quick tutorial about using the Zend_Mail component of the Zend Framework to send both normal, plain-text emails and ones with MIME attachments.

Using PHP's built in function (aptly named mail() ) is relatively straightforward - until you need slightly more advanced features, such as adding and encoding email headers or sending multiple mails efficiently. Fortunately, the Zend Framework comes with a very capable mail component called Zend_Mail.

He shows how to send a simple email, do something a bit more complex with a custom SMTP server, read messages from a remote POP3 email box and how to attach a binary file/message.