Squirrelmail (en)
From OnnoCenterWiki
SquirrelMail is a standard web-based email package written in PHP. It includes built-in pure PHP support for IMAP and SMTP, and all pages are created purely in HTML 4.0 (without the need for JavaScript) for maximum compatibility across browsers. It has very few requirements and is very easy to configure and install. SquirrelMail has all the features you would want from an email client, including strong MIME support, address books, and folder manipulation.
