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
We have an on-premise SMTP relay that users an O365 connector to send email via O365 both to internal and external recipients.
Our connector uses the hosts IP and our configuration satisfies 1.b and 2. of the new requirements.
I've also analysed email headers and message trace logs and determined that the Return-Path and From/Sender domains are the same and are owned by our organisation.
Hence we should not be impacted.
However we do have a few systems that send via the relay from a sub-domain of that of the relay, hence the From/Sender domain and the Return-Path are both the same but are sub-domains of the relays e.g. sub.relaydomain.com.
The sub domains are not published in O365 but the parent domain (the same one as that of the relay) is.
Will this use of sub-domains cause any issue with our IP based connector, is the matching strict or relaxed?
Best regards
Owain