Chapter 4 FortiOS Carrier : MMS Security features : Sender notifications and logging : Replacement messages
  
Replacement messages
FortiGate units send replacement messages when messages or content is blocked, quarantined, or otherwise diverted from the receiver. In it’s place a message is sent to notify the receiver what happened.
With FortiOS Carrier MMS replacement messages, send and receive message types are supported separately and receive their own custom replacement messages. This allows the network to potentially notify both the sender and reciever of the problem.
For example the replacement message MM1 send-req file block message is sent to the device that sent one or more files that were banned. The default message that is sent is This device has sent %%NUM_MSG%% messages containing banned files in the last %%DURATION%% hours. The two variables are replaced by the appropriate values.
Replacement messages are not as detailed or specific as MMS notifications, but they are also not as complicated to configure. They are also useful when content has been removed from an MMS message that was still delivered.
For more information on replacement messages, see “MMS Replacement messages”.