While doing testing with integration partner for AS2 implementation using Logic Apps, if you are clueless when partner mentions that MDNs are not getting processed in their system despite having all the correct settings, then this post might be of some help to you.
We faced this issue when we tested following scenario with one of our integration partners. Following was the scenario:
The AS2 agreement was configured for sending Signed and Encrypted MDN messages in our system.
We recently migrated this AS2 agreement from BizTalk server and this configuration was exactly same as it used to work with BizTalk server.
After two days of long testing and debugging hours with partner and trying out different permutations and combinations to isolate the issue, we got this working only when we added some text in MDN Text box in Agreement Receive settings as highlighted below: