We have recently moved from exchange 2010 to exchange 2013. Ever since our move we have not been able to get message approval notifications.
We had it setup on exchange 2010 if a user sent an email to “All” it would get sent to a list of moderators for approval. Since the new exchange server went in I have been applying a workaround to allow emails to send out for users (adding them into the do not need approval box).
To me it looks like Outlook is sending the email to Exchange 2013 then Exchange 2013 is trying to send the email to Exchange 2010 for delivery.
I have tried creating a new distribution group in case some of the permissions were lost in the move, but it doesn’t work either.