SquirrelMail is a PHP4-based Web email client. It includes built-in pure PHP support for IMAP and SMTP, and renders all pages in pure HTML 4.0 for maximum compatibility across browsers. It also has MIME support, folder manipulation, etc.
The 1.2 series of SquirrelMail is getting more and more rock solid. Lots of bugs have been fixed. Support for international users and php 4.1 has increased significantly. See the changelog: http://www.squirrelmail.org/changelog.php download now from http://www.squirrelmail.org/download.php