Set up forwarding address in Office 365

Go to Exchange admin in your Microsoft / Office 365 admin and follow these steps:

1. Select Recipients on the left menu
   
2. Select the Contacts tab
3. Now click the plus sign and select Mail user to add a new mail user
4. Fill in the details (see screenshot below). The external email address will be where the email is forwarded to; the password is only important if you want to give the user some access (for example to shared mailboxes).
5. Wait! (Up to 1-2 hours)