AS2 aka Applicability Statement 2 communication protocol, one of the most widely used secured protocols used in the B2B world can sometimes be very tricky to troubleshoot, especially when you are trying to set up a new connection with your trading partner.
There can be numerous different reasons why your AS2 setup may not be working but in this particular article we are only going to talk about the error "insufficient-message-security" which comes in a negative MDN originated from the receiving party.