Workflows in CRM 4.0 can send emails to users that are local (on the domain), but as soon as we try to send emails to users outside the domain (to a gmail account for instance) the email doesn't get sent.

Instead, we just get "The message delivery failed. It must be resubmitted for any further processing."

The email router says SMTP sends work just fine. What gives? How do we fix it? Or at the very least, how to I troubleshoot this?