Mac Mail not downloading emails

Hello. My mac mail is not working. It appears to be an issue with the Exchange 2007 server. The only way I can access my emails is via Thunderbird (which stinks). Neither Mac Mail nor Outlook will download my emails.

Connection Doctor status: Mail was able to connect to the internet.

I see that this is a common problem for many other folks. Has this issue ever been solved? I have spent a considerable amount of time on forums, talking to Apple Support, and Google searching -- no luck finding a solution. Its very frustrating -- I am using Thunderbird to get me by for now. I have a new Mac, Lion 10.7.4.

Help!! Thanks.