We are facing same issue as well, to setup Auto-Submitted email. @Anonymous
Since graph API to send email can be used by Flow (Power Automate) or any other code to triger automated email. What we don't want is email loop been caused when email sent out by automation.
We could technically use X-Autoreply, X-Autorespond, X-Autoresponder. But more align with RFC-3834 is better. Since there will be more bots supporting Auto-Submitted than X-
prefix one.
For example Zendesk, FuseDesk, those ticketing system are ignoring email with those header to avoid infinite email loop.
This is as simple as telling receiver, this email is notification email, generated by code not by human. Do not respond with out of office, or new ticket from ticketing system etc.
I know some may suggest no-reply email to send email, for us we are trying to send email on behalf of user, we want human to reply not bot to reply. That's why we are looking to add this header.