We have the same issue, but in our case we use Exchange Hosted Filtering for the email scanning. We are supposed to put all of the IP addresses in the always allow area of the external connector for Exchange. Because TMG re-applies the default
configuration every couple of minutes, the addresses don't stay. What happens now is that when we get a lot of mail at one time, TMG assumes there is an attack from that IP and blocks it for an hour until it resets automatically. Our server ends
up blocking legitimate mail. If I thought it would be of any value to pay the $99 to MS I would, but it seems like a lot of people have already done so.
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