An outside non-Exchange email provider is the MX record for the domain like abc.org. The provider forwards/aliases some users and has mailboxes for others. The local on-site Exchange server POPs email from those mailboxes. When an internal Exchange user sends email to an alias at abc.org, it fails because it cannot find the user on the local Exchange server and does not forward to the outside provider when no internal user is found. How can I handle that situation?