Updated Requirements for SMTP Relay through Exchange Online

Carolyn_Liu I still have trouble understanding rather I am affected or not. On the post, the following is said:

"If you need to use a third-party add-on service to process email messages sent from your organization and then relay through Exchange Online, the third-party service must support a unique certificate for your organization, and the certificate domain must be an accepted domain of your organization. An example is that your organization uses a signature service to add signature/disclaimer for each email sent from your organization"

In this case, a signature service would have no reason to change the P1 sender, as it behaves as a simple SMTP relay. It would still be the original one. Even in the case of a setup using IP validation instead of the certificate one, how would this change affect the workflow? The return-path header would still correctly point to the original P1 sender - the actual user inside the organization.