Receives an **asynchronous MDN**: a partner POSTs the receipt for a message
we sent earlier (AS2 async mode). We match it to the tracked delivery by Original-Message-ID, verify the disposition and — recomputing the MIC from the…
POST
we sent earlier (AS2 async mode). We match it to the tracked delivery by
Original-Message-ID, verify the disposition and — recomputing the MIC from
the delivery’s stored payload — the integrity check, then flip the delivery
to delivered (or failed with the partner’s reason). Unauthenticated by
AS2 design; the match is to a Message-ID we minted, and a signed MDN must
verify against the partner’s configured certificate before it can change
delivery state.