I have an Exchange 2003 that can handle emails for two domains alpha.com (default), beta.com (secondary). I have a user who I changed his default email to beta.com. When he writes his email with his Office 2010 Outlook and change the "from" field to his alpha.com email domain. He immediately receives an email saying "you do no have permission to send to this recipient. MSEXCH: MSExchangeIS:/DC=m/DC=alpha:servername
This is regardless of who he is sending the email two. Emails send from his default beta.com domain works just fine.
Any ideas how to allow this user or any other user for that matter to be able to send from either domains just fine?