Hello TechNet,
We have 4 Exchange 2013 servers configured in hybrid mode with Exchange Online. All mailboxes have been migrated to the online service and the MX records points to Exchange Online.
The purpose of the on-prem servers is for management and SMTP relay for printers and applications.
When we send e-mails to distribution groups that are not synchronized from AD or public folders that wasn't migrated (they were created in Exchange Online) via the SMTP service on-prem, they get discarded with a 550 5.1.1 RESOLVER.ADR.RecipNotFound message.
I suspsect that this is related to how accepted domains and send connectors are configured in Exchange 2013, and I would be very grateful to get some input on how to configure this correctly for our scenario.
- Our default mail domain (xxx.com (no not actually)) is configured as "Authoritative" on-prem, and as "Internal Relay" in Exchange Online.
- The scope of our send connector "Outbound to Office 365" only contains "xxx.mail.onmicrosoft.com".
What I would like to do is to re-configure our default domain to "Internal Relay" and add xxx.com to the scope of the Office 365 send connector.
My concerns are that this will break mail flow in any way or that it may cause an e-mail loop when sending to non-existing addresses.
Any input on this matter is greatly appreciated.