If you’ve read 5ThirtyOne’s post about setting up Apple Mail with GMail’s IMAP you may be enjoying iPhone goodness and be all happy. But you may also be miserable about the fact that GMail’s implementation of IMAP fakes your IMAP folders based on your labels in GMail, which means you end up with duplicate messages in Mail.app.
Personally I think labels make much more sense as they’re more like smart mailboxes, where you don’t have a duplicate of the message, but rather a flag saying what it concerns. The problem is that if you like to locally cache your IMAP mail for offline viewing, you’ll end up with hundreds of duplicate mails in Mail.app because Mail.app thinks that a message in a label ‘folder’ on GMail is distinct to the version of it in GMail’s All Mail folder (your mail archive on GMail).
Some mail clients, like the powerful but ugly Thunderbird, seem to have more comprehensive settings to subscribe or unsubscribe to certain folders on IMAP servers (and I’m not sure how many people know you can do that in any case). So the solution would be to unsubscribe GMail’s All Mail folder and you’d be fine.
Alas, not only is the subscription/unsubscription is in a relatively obscure place in Mail.app (highlight the mailbox and Get Info brings up the window with Quotas, Mailbox Behaviours and also the Subscription List) but also Apple’s IMAP subscription doesn’t seems to work on almost all IMAP servers, including GMail.