In this new tutorial from the IBM developerWorks site, they take a look at the development of a webmail interface with the help of PHP.

You know how to get users to interact with a PHP application using a Web form, but sometimes e-mail is just more convenient. Maybe your users are using small devices like cell phones or interacting in a way that's not real time, such as subscribing to an e-mail list. Find out how to read and send e-mail by building a PHP Webmail application.

They cover connecting to the server, grabbing the information from a specific email inbox, pulling the data for a single message, deleting emails, getting a list of the current emails, and how to work with attachments and multipart MIME messages.

You'll need to log in to get to it, but it's a great example of how to work with email in PHP (more than just sending them with mail() or PEAR's mailer package).