we are in the middle of a side by side upgrade of our on-prem Exchange servers from 2016 to 2019. The mailbox server and the hybrid server have both been successful with their 2016 counterparts readying to decommission. But each time i attempt to put the Exchange 2019 EDGE server in play, email from Exchange Online mailboxes is bounced back with "550 5.7.54 SMTP; Unable to relay recipient in non-accepted domain" no matter what destination. The process followed is:
1. remove Edge subscription from Exchange 2016 Edge and answer yes to remove synced objects
2. remove Edge subscription from on-prem Hybrid server
3. create new Edge subscription on the 2019 Edge server to create the xml file
4. copy xml file to Hybrid and create new Edge subscription on-prem. Hybrid will be the sync server for Edge.
5. Run Hybrid Configuration Wizard on the Exchange Hybrid server with the option checked for Central Mail Transport (requirement by the mail gateway keepers, not my first choice)
On the surface, everything looks as it should, the Edge sync shows Success for status, the new connectors are there for Edge and O365 to on-prem and vice-versa. We can send email from external and on-prem mailboxes up to our users in the cloud on Exchange Online without issues. But any email, whether to arccorp.com (our primary domain) or to any other domain is bounced back within a few seconds.
Same procedure is followed to fail back to the Exchange 2016 Edge server. And email starts to flow again in both directions.
What am i missing here???
