On Linux 2.2.x, 2.4.x
PHP 3.0.15+ / PHP 4.0.x
Apache 1.3.x
MySQL 3.22.25 or PostgreSQL 7.0.x
Courier-IMAP 0.33+ and/or qmail 1.03 for POP3 access
We have reports of it working on Windows NT and OS/2, and using Oracle as the database.