If your trying to email a distribution group in Exchange 2013 from outside you might get the error below :-
Delivery has failed to these recipients or groups:
Your message can't be delivered because delivery to this address is restricted.
Diagnostic information for administrators:
Generating server: server.domain.local
[email protected]
Remote Server returned '550 5.7.1 RESOLVER.RST.AuthRequired; authentication required'
This error is caused by Exchange 2013 default behaviour of setting distribution groups to only allow emails from internal senders.
To change this setting enter the Exchange Control Panel, ECP.
Go into Recipients, then groups.
Double click on your distribution group with the issue.
Select : Senders inside and outside of my organization and click save
