Uebimiau is an universal webmail developed in PHP. It is free and can be installed in any email server.

-It runs under any System;
-It doesn´t require any extra PHP modules;
-Doesn´t need a database (as MySQL, PostreSQL,etc)
-Doesn´t need IMAP, but compatible with POP3 and IMAP
-Compatible with the MIME Standard (send/receive text/html emails);
-Doesn´t need cookies;
-Easy installation. You only modify one file;
-Compatible with Apache, PHP, Sendmail or QMAIL;
-Can be easily translated into any language (already translated in 17 languages);
-Can use a variety of skins