I haven't tried out sylpheed since gtk-1.2 days. I was looking for a replacement for Evolution which I was using as my second mail client (use Thunderbird as the primary client) .
I wanted the simplest of GUI based mail clients and Sylpheed seems to be perfect fit - Its fast, does most of what a mail clients do (protocols, privacy, junk mail handling, command line options, etc) and more importantly doesn't crash (evolution crashes a lot!). Its a little unconventional in terms of UI, but I guess its manageable.
sudo apt-get install sylpheed