resp Inbound Msg Id

1.3.6.1.4.1.334.3.1.2.3.1.12

The unique message identifier that the 'previous hop' MTA assigned to the message. If the 'previous' MTA uses a different messaging technology or identifier scheme, this identifier serves to correlate the message from MTA to MTA. If the 'previous' MTA uses the same technology, this value is generally superfluous. If this is the first MTA in the delivery sequence, or if the previous message id is unknown, this variable is null-valued.