I would vote for Eudora - have been using it for years and it doesn't have the security risks associated with Outlook (have you noticed? all the really malicious viruses recently have exploited Outlook's weaknesses). It handles multiple personalities absolutely transparently. Now comes in two flavours - a version you pay for (no ads) and a free "sponsored" version (unobtrusive ads bottom left of screen which I don't mind at all). You do need to register for both versions. Rel 5.1 just announced.
------------------
Feline
(I Sit, I Watch, I Smile)