Forum Discussion
Exchange - Undeliverable Emails
Which server is generating the NDR? It might be a simple case of you having a matching contact within your directory, causing the message to be routed incorrectly. Also, run a message trace: https://docs.microsoft.com/en-us/microsoft-365/security/office-365-security/message-trace-scc?view=o365-worldwide
Thanks for the suggestions. I had a look at the https://protection.office.com/ message trace utility and I wasn't able to run it but I think it shows where the problem is.
I'm logged in as mailto:xx@domainname.onmicrosoft.com but the default queries in the message trace section all refer to mailto:xx@domainname.onmicrosoft.com clearly the system is somehow confusing the two accounts.
My primary Microsoft account (for Microsoft 365, Onedrive etc) is under mailto:xx@domainname.onmicrosoft.com . the Exchange account is (because it has to be) under mailto:xx@domainname.onmicrosoft.com .