Exchange hybrid environment - routing questions.
Hello!
Yesterday I found problem with sending mail from on-promise mailbox to M365 group ended with NDR recipient not found.
As far as I did reaserch the case is in domain setup as Authoritative. I also looked up at Exchange Hybrid Environment - Internal Relay vs Authoritative? : r/exchangeserver topic.
I made a workaround and created mail contact with M365 group address without syncing it to the cloud.
I have a few question:
- Am I right that I have to change Authoritative to Internal Relay for our default domain to resolve the problem?
- Am I right that I should do this change in on-prem. In cloud leave this domain as Authoritative? If yes, which option should i choose? External relay domain/Internal relay domain/Authoritative domain
- What should I check before change? I have read that mailloops can occure and some delays / NDR problems after change setup.
- Is this change fully revertable if any problem occures?
- Is that okay to change only default domain and other domains leave as authoritative?
- Because of curiosity: why in the current setup (with two authoritative domains) does sending an email from on-premises to a Microsoft 365 group hosted in the cloud result in an NDR, while sending an email from the cloud to an on-premises mailbox (not synchronized to the cloud) works without any issues?
Current config:
2xExchange Server SE in DAG
Hybrid Environment with Entra Connect and Exchange Hybrid
2 connectors between On-Prem and Cloud Exchange
All domains setup as Authoritative in On-Prem and Cloud Exchange.
Thank you in advance for every response and wish you good day.
