First question: personal or business use?

At work, most Windows users are on Eudora. Seems to go pretty well, though the app does have its warts. Fortunately it's Unix-compatible mbox format underneath, so you can access your local mail with a wide range of tools.

I checked on this last week, Evolution isn't ported to Cygwin. KDE has just been, but it's still a bit raw (trans: I couldn't make it work) and slow (per others). Several of the command-line / console mailers work in Cygwin, including mutt.

Mozilla offers a mail client, if you care to go that route. One person's list of [link|http://w3.hethmon.com/os2isp/1999/Aug/Msgs/l2w57452.html|mailer identifiers] turns up PMMail, MR/2, & Pegasus Mail. [link|http://email.about.com/cs/winclientreviews/|Another list of mail clients].