We have the best email client: Yam
I'd object to that - YAM doesn't have IMAP support yet, does it?
For someone running their domain's mailserver - I would say that IMAP is pretty darn important! (Especially after you have tried IMAP - then POP is very uninteresting).
So it would also be nice to see a port of Mozilla's mail client (and it has improved A LOT lately) ;-)