Question:
User A replies to an Email from User B.
User A gets the email rejected and the error message
"You can't send a message on behalf of this user unless you have permission to do so."
The FORM field has been changed to User B and thus rejected.
I have examined the transaction logs and all appears that user A is trying to send an email on an account that he does not have sufficient rights. Next I check the message itself and sure enough the sender is User. Exchange appears to be behaving normally.
Users both are using Outlook 2010.
What could cause Outlook to change the field? Could it be an issue with the X400LegacyExchangeDN settings for the users?
Cache has been cleared and problem is intermittent. Not all emails replied to from A to B are rejected. Most go through. User doesn't have issue with other users.
Turning off cache resolves issue.