Before switching to Linux I had a stint with the Bat! for about 10 months. It is by far the most USEFUL email client I have used. I was able to create boiler plate text for a variety of situations that was easy to add to an email, filter mail into folders…but also have those folders play unique sounds (or wav files) when I received messages in them, search very quickly through all my messages, and probably a dozen other cool features that I’ve since forgotten about. It was fast and lightweight, never taking up more than 6MB of memory while running.
I wish the Bat! was ported to Linux, and I’ve made suggestions to the developers that they do so. I would gladly pay for a second copy on that OS.