The Bat! is an e-mail application that features support for multiple POP accounts, true multithreading, MIME and UUencode standards, message notification, PGP support, APOP authorization, message sorting, message templates, minimization to the system tray, and multimedia support.
Designed for the USB-flash disk.
The Bat! has the following other editions available: The Bat! Professional and The Bat! Home.
This is the only program I have seen which gives multithreading sorting in the mail client (except our favorite GMail which gives it online..) I am real fan of this tool.
I am not able to put its screenshot right now, but will capture it and put it in a short time (as I get some time to install it !!)
Here is the screenshot..
You can donwnload it here