Exchange Online mail flow - forward emails with no mailbox to external receiver




I have a question. I would like to set my mx to point to Exchange Online.

But I have a lot of email-addresses that do not have a mailbox in Exchange Online / Office 365.


Is it possible in Exchange Online to create a "default" email flow that says "If there is no matching mailbox in Exchange Online / Office 365, then forward the email to SMTP server xxxx" ??


If so - any hint on how to do this?


Br. Rune Myrhaug

Uninett AS

1 Reply
best response confirmed by Rune Myrhaug (Contributor)

You have two options for that scenario. First one is leave the MX pointing to on-premises and configure the domain as "internal relay" in O365. That way, Exchange Online will check for the presence of specific email address against the ExO GAL and if no match is found, will route it to where the MX record points at.


Alternatively, you can create a connector to route messages sent to specific recipients, either on a (sub)domain basis or by using a Transport rule. Check the documentation here: