When moving to Exchange 2010, I also needed to move my BES server.
Part of the requirements for BES was to download and install http://www.microsoft.com/download/en/details.aspx?id=1004
on my Exchange Server.
I did this, and then later was told I shouldn't run the BES on the same machine as Exchange, so I created another virtual machine for BES. I have been having some issues with sending email on my exchange server. I have users that have multiple email accounts, and use our server to send all email.
Under the above setup, these users were able to send and receive email without any issues when we were on exchange 2003.
Now, under exchange 2010, they can receive email from both accounts, but they can't reply to email received from "email@example.com"
I've gone over the "send as" permissions, and there doesn't appear to be a way to grant permissions to an account that isn't part of my domain.
Is there a possibility that this Messaging API and Collaboration Data Objects installation is causing these issues? If so, what's the best way to remove the software/repair exchange?