Hi
I have a feeling that PocoMail might run in Wine on Gnu&Linux or Mac or whatever. If you already do have something you trust then stick with it. MS stuff seems to be really tricky to get working in Wine but most other stuff works quite well. It's a bit hit&miss and sometimes takes a bit of work but they have forums to help (they aren't very noob-tolerant tho). In Gnu&Linux it's better to try to stick to Gnu&Linux programs but it's not essential! Apparently some Windows programs (err, games tbh) have run faster under Wine than they ran on Windows!
I'm not sure what Ubuntu's plans are for email and calendar. There are several rumours flying around but i like the idea of staying with Evo even tho i don't use it myself! They seem a good bunch.
Anyway this is all a lot off-topic! If you have something good then stay with it!
Regards from
Tom