SquirrelMail is a basic web mail program you can use to access your email. If you are used to using SquirrelMail for your email you can keep doing this or try out Horde. All of your email that is in SquirrelMail is in Horde as well.
Horde Mail Login
Horde is a full featured web mail program you can use to access your email and also manage your calendar and tasks. If you have been using SquirrelMail, this program will allow you to access all of your email that is in SquirrelMail but will also offer some additional features.