Step 1. In order to forward mail externally for an ‘Exchange Mailbox User’, you need to create a ‘Contact’. A contact is an active directory object (not a user) that has an email address. Log into Exchange Admin Center > Recipients > Contacts > Add > Mail Contact.
Step 2. Create a contact and give it an understandable name so when it appears in the Global Address List it’s obvious what it is for (e.g. Hitch AP Inbox)
Step 3. Navigate to the Mailbox Tab, locate the account or user you want to setup forwarding for, and edit them.
Step 4. For user selected in [Step 3], go to Mailbox Features > Scroll Down to ‘Mail Flow‘ > View Details > Tick ‘Enable Forwarding‘ > Browse to the contact created in [Step 2] you created earlier > OK.
Step 5. Select “Deliver message to both forwarding address and mailbox” if the user/account would still like to receive a copy of the message.
Step 6. Save all changes.