Moving to Linux - what email is best?

I am changing my server at work to Linux and now I have an excuse to abandon lots of Windows apps. I'm particularly looking forward to abandoning Outlook email.

Dear builder.commers, what do you think is the best email client out there; one that has html and text features. Particularly one which is more flexible than Microsoft's options.

Thanks in anticipation.

Ry Robinson
ryrobinson@lycos.co.uk