Acknowledgment Messages

The acknowledgment is sent by the MT service to Logical Terminal to confirm the receipt of a message and its safe storage by the service.

If an ACK is returned, the message is accepted by the MT service for delivery to its destination. If a NAK is returned, the message, though safely stored, is not accepted for delivery. The structure of an ACK or a NAK message is the same, except that the value of tag 451 in the text block of an Acknowledgment message. 0 indicates the ACK, and 1 indicates the NAK.