It supports multiple users, accounts, and IMAP/POP inboxes. Moreover, the interface is very simple and includes floating toolbars that you can modify freely.
The Bat! is especially designed for accounts with a large amount of messages, backed by its powerful engine that provides very quick results. It incorporates a powerfully advanced message and notification filtering system so you can always know if you have received an email.
The program includes an automatic spell checker, supports all PGP versions, and organizes all your messages into folders similar to that of Explorer.
30-day trial version.