Tiger Mail And Exchange


I've been using Mail.app in Panther with our company's exchange server since day 1. Since upgrading to Tiger, Mail has continued to work for us, until last weekend. Mail still works for all POP accounts, but any new mail coming into the Exchange account does not show up in Mail. The mail is arriving, as I can receive it with Entourage and webmail in Safari. The Mail.app connection doctor says it couldn't connect to the Exchange Server - "check your network connection and that you entered the correct information in account preferences". The settings are correct - the same as they have been when it was working. When I tried to set up a brand new account as an IMAP account, it brings in the exact same list of mail messages that Exchange account shows - they all stop on May 26th. Anything newer doesn't show up. Any messages I send with that account go out, but don't show up in sent items either. Basically, it seems like it stopped synchronizing on that day. We have two Macs that this happened to at the exact same time. The day that the mail stopped coming (sounds like a country song), IT rebooted the exchange server. That is the only known change. We had already updated mail to 2.0.1 long before this happened.
I'm looking to get mail and exchange back on speaking terms. Anyone else experienced this problem? Know any solutions?
After much effort and gnashing of teeth, our IT guys figured out that the problem was NOT with Mail, but that when they rebooted the Exchange Server, it turned off (somehow) IMAP - which Mail requires to work with the Exchange Server. They turned it back on, and all the messages came back and we're as good as new.
I'm having the same problem, however IMAP is still active on the exchange server. If I bring up the "Mail Connection Doctor" the exchange account always is able to connect to the server successfully. Sometimes it takes MUCH longer than it should. So when I try to get new mail, some of the exchange information syncs up but it will time out before I can even view all or read any emails.

any advice?