Exchange 2013 - Inoltrare un messaggio ad un indirizzo esterno

A differenza della versioni precedenti l'unico modo per abilitare l'inoltro di un messaggio verso una casella esterna è procedere con un comando di PowerShell

Here is what I have to do:

1. Create a contact in the Exchange 2013 "Admin Center".

2. If you want keep and forward, From Exchange Management Shell: 
Set-Mailbox -Identity "Allen" -DeliverToMailboxandforward $True -ForwardingSMTPAddress "allen@externaldomain.com" -ForwardingAddress "allen@externaldomain.com"

2a. 2. If you want to forward only, From Exchange Management Shell:
Set-Mailbox -Identity "Allen" -DeliverToMailboxandforward $False -ForwardingSMTPAddress "allen@externaldomain.com" -ForwardingAddress "allen@externaldomain.com"

If you go back into the Admin Center and look at the properties of the Mail Flow, Forwarding, you will see your Contact listed.