We are sending a document to a TP. Immediately, in TN we see the MDN with the content just “Connection: close”. Naturally, our processing of this fails, as it does not contain sender/receiver.

TP says they see nothing on their side.

Could it be anything on our setup? Since it’s MDN I think it’s their issue, but I am not too familiar with this.

Thanks,
I. Jamal

Do you receive a real MDN (with header etc.)? or just that “conncetion: close”?
If it’s later case, your request is not reaching your client’s internal system, which should generate a proper MDN.

Check with your network team and client side for:
if any Proxy/Load balancer that’s blocking the connections on your side or client side.
That error doesn’t seem a WM system error, must be some other in-between system that is trying to connect to the destination system, and failed.

Yes I would say a more troubleshooting is required for this and enage your TP and network folks if needed to make sure no transport layer/DNS issues back and forth.

HTH,
RMG