Resource Not Reachable Externally?

Our first attempt at emailing our Resources externally is proving unsuccessful. Please forgive if this is an obvious fix but not readily finding the solution and we're under the gun. Attempting to reach a Resource via its "Allowed EMail Address" in ConsoleOne externally w/no luck. Internal is fine. Doesn't seem to be caught in our spam filtering, nor bouncing back to originator.

Any suggestions would be appreciated.