I have been using Windows Live Mail for some time now. Considered the heir of Outlook for Vista OS, it can also be downloaded for XP OS.
It looks good and it works OK. You can download your POP and IMAP accounts and also it has a reasonable RSS reader.
I only see an inconvenient: you must have a hotmail / msn account. If not you cannot use it.
You can read: Winplanet (E), Softonic (S).