@ko-lem Thanks for posting, I think you are on the right path. Let me try to clarify:
-
grant.ahas two messages: 1) outreach and 2) customers reply (reply_to_message_id) -
grant.bdoes not have any messages
So only grant.a can respond using reply_to_message_id since its only in their inbox. So grant.b cannot use the same reply_to_message_id since its not in their inbox.
So what you are saying makes sense.