The Bat! - description from Softdepia.com:
The Bat! is a powerful, highly configurable, yet easy to use email client. We've designed it especially to help you deal with your growing volume of emails as quickly and efficiently as possible, saving much of your precious time. Use all its powerful features at home or at the office to handle your email naturally - the way you want and how you want, simply and directly.
Support for an unlimited number of accounts and users
Fully customizable message templates that save hours of typing
Powerful filtering for automated message handling
Support for S/MIME and PGP versions from 2.6x through 6.5
Mail Dispatcher for managing email on remote servers
Simultaneous mail processing in the background for all accounts
Familiar Explorer-style folders for organizing messages
Easily configurable user interface with message preview option
Built-in HTML email viewer and message editor with spell-as-you-go
Sophisticated address book for storing all personal information
Unique Mail Ticker? for email notification
Multi-lingual interface supporting 15 languages on the fly
Import message bases from all major email clients
Many more features for managing email quickly and easily...
The Bat! is a "Free to try" program. You can download and try it for an evaluation period.