Chapter 4 FortiOS Carrier : MMS Security features : MMS virus scanning : Removing or replacing blocked messages
  
Removing or replacing blocked messages
To remove blocked messages, expand MMS Scanning and select Remove Blocked for the selected MMS types.
Select Remove Blocked remove blocked content from each protocol and replace it with the replacement message. If FortiOS Carrier is to preserve the length of the message when removing blocked content, as may occur when billing is affected by the length of the message, select Constant.
If you only want to monitor blocked content, select Monitor Only.