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.