All user accounts have a primary domain address and an alias address (different domain)
Some users need to send emails from the alias address, but Exchange does not allow sending from your non primary address. I always receive an undeliverable when trying this in Outlook.
So, I have removed the address from the user's record. Created a distribution group and added the address to that group. Added the user as a member of the group and granted Send As permission to the user for the group.
Why, when I they try to send emails via Outlook from the distribution group does Exchange return an Undeliverable...
"You can't send a message on behalf of this user unless you have permission to do so. Please make sure you're sending on behalf of the correct sender, or request the necessary permission. If the problem continues, please contact your helpdesk."
Thanks in advanced!
p.s. It has been over 12 hours since the group was created.