We have an environment with 2 separate domains joined by a two way trust. each domain has it's own exchange environment. I have a user who has AD and Exchange accounts in both domains. This user needs to log on to a computer in Domain A with an AD account that is also in Domain A and use his mail account in Domain B. I setup Outlook to connect to the Exchange server in Domain B and use his mail account in Domain B. Outlook opens fine and his inbox populates with email sent to his account in Domain B. So the receiving part of the configuration works fine. However, he is unable to send email to any account on any domain. Even online accounts such as Yahoo and Gmail. I checked the properties of the AD account in Domain B and his Domain A account has the "send as" permission.
What Am I missing?