Mac Mail problem

I have a problem with Mac Mail and I was hoping that someone here might have
seen this sort of thing before and might come up with an answer.

I have a Macbook running Snow Leopard. Having used my iPhone to connect to
my server at work (Microsoft Small Business Server 2008) and synchronise my
mail and calendar, I assumed this ought also to be possible with my Mac
laptop.

So I added a new account to Mail: mailgate.[domain] with username and
password. Under "account type" I chose Exchange 2007. The mail program
attempted to synchronise with the server but downloaded only mail up to last
August and I couldn't find a way of making it download recent mail, so I
decided to give up and delete the account.

However, for some reason it seems to be impossible to delete the account
properly. I have deleted it from the list of accounts in Mail but now
whenever I use Mail the application hangs for 20 seconds or so and I get a
message telling me that the computer is trying to connect to the SBS server.
Whether I click Cancel or Continue, the message keeps coming back, after a
few minutes.. And no mail is downloaded.

I thought perhaps some files on the Mac had become corrupted so I tried
running Disk Repair, from my startup DVD, and although that corrected
various errors it didn't correct this particular problem. I also purchased
the latest Disk Warrior and ran that, but although it reported that it had
successfully built a new directory (or whatever the correct term is) it
hasn't cured the problem either.

Are there some particular files on the Mac that I ought to delete? Is there
a way of sorting this out that doesn't involve a system re-install? Thanks
in anticipation of any suggestions.