Unbounded growth for mail.app/IMAP users

[tachijuan]

I have a couple of Mac users that have multiple machines using Mail.app to get their mail via IMAP. For these users, if they leave Mail.App running on their desktop and their laptop, all of their mail gets downloaded multiple times. One user has 20gb of mail. Over a two week period his usage on both machines has gone to >160GB. We've deleted the account on both machines and re-added them. If mail.app is only running one machine at a time, the multiple download thing doesn't happen. However, if the user forgets to shutdown Mail.App on his desktop before he goes mobile, it starts downloading all the mail again multiple times.

This behavior is not exhibited with IMAP on other mail services (gmail, exchange, etc.).

Has anyone run into this? Any ideas as to what's happening? Any suggestions for how to fix it?

We are running the latest version of GA code on the zimbra server.