Update 11/13/2023: We added new information on how to know when this change is released to your organization.
Today, we are announcing an update to our requirements for SMTP relay through Exchange ...
Updated Feb 22, 2024
Version 19.0
Blog Post
Thanks Carolyn_Liu
"Yes, subdomains are not considered as accepted domains in sender case."
1)Just to re-clarify ,our scenario is there are two connectors configured in EXO tenant(The accepted domains are mycompany.com)
O365 to Your Org(Outbound connector to a email server)
Your org to O365(email server to Exchange Online)
An email is sent from user1@test.mycompany.com to email address removed for privacy reasons
.Will the relay fail?Can you please confirm?
2)I tried to test this scenario by adding a sub domain- test.mycompany.com using POST REST API : https://graph.microsoft.com/v1.0/domains (but it automatically got added as an accepted domain) and send an email from user email address removed for privacy reasons to an external user, the relay was fine.
I would like to understand in what scenarios an email can be sent from a sub domain that is not an accepted domain in Exchange online? (Because if i add a domain in Microsoft Admin center its automatically added in accepted domains.)