Within a Distribution Group an approval workflow and email is generated, when you open Outlook as the approver you receive the error message below and the approve/reject buttons are dimmed
"This request cannot be approved or rejected for the following reason(s): The sender (FIM Service Component User) is not an authorized sender of approval requests. Contact your system administrator for assistance."
The FIM service account email address entered during the FIM Extensions and Add-ins install/configure process was not correct. In my case when this was encountered, I entered the email address correctly for the FIMService account; however Exchange created a different PrimarySMTP address for the account, and set other as a secondary. This caused the error.
On the machine with the FIM Extensions and Add-ins installed, perform a “Change” on the installation.
Program and Features > Forefront Identity Manager Add-ins and Extensions > Change
During the change, enter the correct email address assigned to the FIM Service account.
Hopefully you discover this before deploying company wide. If not, you can always make the change via Group Policy, or other Desktop management solution.