Looks like there is lots to think about when choosing an email client on the Mac platform … no different to Windows in that respect.
All E-Mail Sucks
That’s the only really truly awkward transition I’m facing: How to get my mail from my Windows client to a future Mac client?
I’ve been using the awesome (but flawed) TheBat! for as long as I can remember (that’s 1997). This means the mail database is locked into a proprietary format.
Ugh … I’m not gonna think too much about it now, or I’ll scream.
Another reason (or: nail in the coffin) for turning away from commercial/proprietary formats and to open-source file formats.