I got a company who has a 2003 exchange server. They have 3 email domains on the server. They can receive email just fine to all 3. A couple users have to be able to send from the different domains. They can send from there primary default address just fine. Example firstname.lastname@example.org
They have outlook 2010 which allows them to set a FROM address. If they try sending a email from email@example.com or firstname.lastname@example.org they get a bounce back saying.
You do not have permission to send to this recipient. For assistance, contact your system administrator.
Any ideas why this would be?