I've been using PowerMail since 1998. Every so often I get a bit frustrated with its IMAP handling, and go and have a look at alternatives, but I find them all pretty dreadful.
For my work email I use Apple Mail - it does IMAP very nicely, but I heartily dislike nearly everything else about it. Others seem to be fixated on 'features' such as Twitter integration, and other nonsense. All the same - PowerMail's IMAP support is its weak point. I'd hate to have to give it up for something else, but very good IMAP support is becoming ever more important. Regards, Daniele