This plugin allows you to create a list of users and/or domains that should be disallowed login access to SquirrelMail. It also allows you to block brute-force password guessing attacks, although please note that this will ONLY help fight such attacks in the SquirrelMail interface, and should really be implemented in your mail system's authentication backend.

SquirrelMail is a standards-based webmail package written in PHP. It runs on top of any IMAP server.