Thunderbird from Mozilla.
I just started a new job and have been traveling back and forth to Burlington, Ontario. I’ve never been a fan of WebMail and wasn’t about to use Outlook anywhere near my mail server, so I decided to take Thunderbird for a spin.
It’s awesome. It has pretty good junk filtering, supports both IMAP and POP3 as well as identities which is a must if you use qmail’s dash-extensions.