I'm about 10% through a staged migration from Exchange 2003 on-prem to Office 365's Exchange Online. The question I have is how do the migrated users that are now successfully using Exchange Online send email to the users still on the on-prem server?

When they try they receive an NDR with the error "Remote Server returned '550 5.1.1 RESOLVER.ADR.RecipNotFound; not found'".

I only have the users that have been migrated have an O365 user account. Those who have not and are still on-prem do not have a O365 user account - yet.

How do I configure the setup (in O365 I assume) so the email addresses for accounts that are still on-prem get delivered to our on-prem server rather than just failing delivery because the address doesn't exist in O365?

I did a little reading on similar scenarios and about the 550 5.1.1 error and have now changed our organisations domain in O365 from authoritative to internal relay. And I was required to create an outbound connecter (in O365).

Emails now sent from bob@domain.com (who is migrated and using O365) to barry@domain.com (who is still on-prem and DOES NOT have an O365) account are not coming back with an NDR, but are not being delivered either...

Maybe I have the outbound connecter misconfigured?

Please help if you have any suggestions on how to fix this.

  • and as a note: emails from grant@otherdomain.com to bob@domain.com and barry@domain.com are working fine! – Reece Jul 20 '14 at 0:03
  • Where does your MX point? Have you engaged MS support (free with Office 365)? – BlueCompute Aug 26 '14 at 9:29
  • MX records were still pointing at the on-prem server. I did use the MS support but their response was slow and by the time they got to me with a suggestion I had already resolved the problem. – Reece Aug 27 '14 at 23:19

You need to setup one of the exchange servers as an edge server, ie it needs to receive all email and then forward the email on. O365 is not aware of barry@domain.com mailbox, so you need to setup o365 to deliver unfound emails to your onprem box. Alternatively setup a mailbox for barry on o365 and use pop account from the on-prem to fetch email.


Sorry for the slow reply on this... After a lot of research of similar scenarios, and a little trial and error, I found that while I do need to set the staged migration domain to "internal relay" I do not need to create an Outbound Connector. The Outbound connector is for routing specific mail through an external connector when the MX records are pointing to Office365. Not looking in the local user list and then sending email for non-existent users to the server that the MX records are still pointing to.

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