The Bat! is a powerful e-mail client with lots of features.

Mail Filtering
Toss messages from your friends into special folders, send automatic replies to people from other departments, mark messages from your dear ones with special colours...

Templates
Create Quick Templates by pressing Ctrl+Shift+Q, type the handle of the template you need and press Ctrl+Space - The Bat! will promptly insert text, attach files and make the message ready to send.

Virtual Folders
Find all messages from/to a particular person for a specific time period and keep search results for further references in a Virtual Folder.

Spam filtering
Use BayesIt! anti-spam plug-in to filter out virtually all unwanted mail while messages you need get through.