[beastcoast]

AS2 is interesting because it includes a cryptographically signed Message Disposition Notification (MDN) - whenever there's a question if a document was delivered, just give the MDN information to the partner. This has led to some interesting troubleshooting sessions, where it turns out that the message failed somewhere in the partner's system, and the only way for them to dig it out and identify the issue was to check logs for the MDN message ID.

I've also heard that MDNs hold up in a court of law; no idea if that's been tested. But it's a great way to confirm delivery of the payload without having to worry about parsing errors.