Mail not working with Exchange

Hello. My mac mail is not working with the Exchange 2007 server. 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.