The ACK messages on receiving have a simple and compact format. The aim is to have a message as short as possible in order to avoid an unnecessary usage of the network. The title of the message is the title of the original message with a leading "ACK:". Example : ACK:Title of the original message. These ACK messages are true messages strictly speaking. They carry the origin, the destination, the route and the MID but they are of a particular type, the type A (private are of type P, bulletins of type B, etc...). This difference allows the routing of these messages without the lines "R:". This is done again with the aim of avoiding an excessive load by data which are of no use in this case. To keep the compatibility with the existing forwarding protocol, the type of these messages is changed to P (private) if the receiving BBS of the forwarding does not know the type of ACK messages (specified in the SID [FBB- 5.12-ABFHM$] by the letter A). In this case, the ack message will continue on its route as a private message. The ACK messages are of the following form : ACK:Message test. <-- Title of message Msg FD1CDC@F6FBB - 22-dec 17:28z <-- Text of message It tells that the message that you had sent to FD1CDC at F6FBB and whose title is "Message test" has been received in the BBS F6FBB on 22 dec at 12:28 GMT.