firstname.lastname@example.org to forward all e-mail to an external service,
email@example.com. With previous e-mail providers, forwarding was very straightforward (pun intended), but how do we do this in Exchange Online/Office365 as simply as possible?
This is just the same as regular Exchange.
Are you keeping that as a mailbox? If not, then create the account as a Mail User. You will find it under Users, Contacts within the Exchange admin part of Office365. There you can create the user and enter an external email address.
If you want to have the email delivered to a mailbox as well, then create the mailbox as normal. Then go in to Contacts under Recipients and create a contact for the external address. Then on the original mailbox that you created, go in to Mail Flow and choose the Contact as a forward.
First: you need to create mail contact.
Second: you can Enable Forwarding to the mail contact.
You can do it with UI or Powershell. If you need setup email forwarding for many user, you should use Powershell. You can read more here: