Chapter 4 FortiOS Carrier : MMS Security features : MMS file filtering : MMS file filtering blocks messages (not just attachments)
  
MMS file filtering blocks messages (not just attachments)
When MMS file filtering finds a matching file in an MMS message, the entire message is blocked. This action is more secure, and can reduce the amount of processing required for that message. For example if one MMS message includes three files, and the first one is blocked then the other files won’t be scanned or attempted to be matched because the whole message is already being blocked.