Chapter 4 FortiOS Carrier : MMS Security features : MMS virus scanning : Scanning MM1 retrieval messages
  
Scanning MM1 retrieval messages
To scan MM1 retrieval messages, expand MMS Scanning and select Scan MM1 message retrieval.
Select to scan message retrievals that use MM1. If you enable Virus Scan for all MMS interfaces, messages are also scanned while being sent. In this case, you can disable MM1 message retrieval scanning to improve performance.