I'm afraid I can't offer much advice, but I have found problems using the mail client with an IMAP server. It tries to download all the messages from the server rather than just getting the headers as normal for IMAP. The server has a lot of messages, and the client stops downloading the messages before it gets them all. If I tell it to get messages again, it starts over from the beginning, stopping at the same point. Basically unuseable!
Hope someone has a hint for both your problem and mine.
Bernie