On-premise Exchange server does not relay emails to cloud-only distribution lists

Steel Contributor



we are running a hybrid configuration. I recently moved 700 distribution lists into the cloud to enable our users to self-manage the distribution lists again, which was not possible between our migration to Office 365 and now.


Unfortunately, I missed the use-case where people send emails to distribution lists via our on-premise Exchange server. Now every relayed email to cloud-only distribution lists returns a "'550 5.1.10 RESOLVER.ADR.RecipientNotFound; Recipient not found by SMTP address lookup'".

How can I enable mail relay to those cloud-only distribution lists from our on-premise Exchange server?

5 Replies

You can create recipient objects for the cloud DGs and configure their targetaddress to point to the domain. You probably would need to exclude them from the DirSync scope to avoid issues with duplicate objects appearing in the O365 GAL as well as duplicate attribute errors.

best response confirmed by Daniel Niccoli (Steel Contributor)

@Vasil MichevI had the same exact idea, but that would be management overhead that we can't handle.


I found a much easier solution actually. This won't work in every environment, but for us it was perfectly acceptable.


We set Exchange Online to be authoritative for our default domain and our on-premise server as an internal relay. Now the on-premise server just sends any email they don't recognize straight to Exchange Online, where the DLs reside.

@Daniel Niccoli Did you need to re-run Hybrid wizard post changing domain type in onprem to internalrelay?


Did you have to change Outboundonly parameter too? or just domaintype was sufficient?

Hi @abkab420, thanks for your reply. I did not re-run the HCW and I do not remember if I had to set the outboundnonly parameter. Sorry, but that was just a long time ago :D