I've been getting bit by Mail getting stuck with "updating cache directory" on just one of my three IMAP accounts (separate providers). Gmail and MobileMe are fine, it is just with FuseMail which uses Microsoft Exchange servers. I have finally found something that may point to the problem:
Azaleos has now spent 6 months working with Microsoft on this issue.
The diagnosis appears to be that significant changes were made to the IMAP protocol implementation in Exchange 2007 that significantly deteriorates the performance of MAC Mail.App clients, especially client with large mailboxes, against Exchange 2007 vs. Exchange 2003.
Although the Microsoft support team’s response has been absolutely exemplary, we have been unable to make the Exchange development team understand the significance of this takeback from Exchange 2003, nor been able to have them implement fixes in the Exchange 2007 stack to address the issue.
More significantly, we have also received absolutely no response from Apple regarding the deficiencies of the MAC Mail.App client, nor even any acknowledgement of the problem. In fact, from the complete lack of response we’ve received, Apple has an absolutely abysmal Enterprise support capability and far worse than anything we’ve experienced from Microsoft.
At this time, Azaleos does not recommend that customers who have significant MAC Mail.App implementations with sizeable mailboxes (in excess of 500MB mailboxes) upgrade from Exchange 2003 to Exchange 2007.
We are recommending to customers that they do upgrade to Exchange 2007. But, that any users of MAC Mail.App move immediately to Entourage or to an e-mail client that implements a solution that is less than 10 years out of date.
CTO, Azaleos Corporation
I'm posting this both as a reference for others and as a question to see if there is a way to resolve this as a customer, other than dumping FuseMail for a non-Microsoft house?