I use Mail.app to read my personal mail via POP and my work email via IMAP. The problem is that my server at work has a lot of IMAP public folders than I am not interested in reading. If you have ever looked in any of the folders, Mail.app will always check the folder for new messages each time it checks for new mail. This is annoying when I am connected via a slow link or simply do not care to check those folders.
There are several ways to avoid unwanted updating of IMAP folders:
ln -s /dev/null ~/Library/Mail/WorkOrders
Even if you click on the "WorkOrder" IMAP folder, Mail.app does not attempt to read the messages so there is no delay. If you ever decide to want to see the contents of the folder again, simply delete the link and Mail.app will update the contents when you next open the folder.Mac OS X Hints
http://hints.macworld.com/article.php?story=20030423151243538