Okay, so Evolution Mail and Calendar is Good Software, too

http://projects.gnome.org/evolution/download.shtml

People hate Evolution because it's a bit of an annoyance as far as
performance goes. While the performance issues are a bit of an
annoyance, I can't say it's worse because it has them.

And frankly, it integrates nicely with GNOME and so it isn't too ugly.
You could try it, too.

//Kristofer "four04" Rye