When the FortiOS Carrier unit identifies an MM4 message as a duplicate message and blocks it, the FortiOS Carrier unit returns a message forward response (MM4_forward.res) to the forwarding MMSC (otherwise the forwarding MMSC would keep retrying the message). The MM4_forward.res message is sent only when the MM4 duplicate message action is set to Block and the MM4-forward.req message requested a response. For more information, see “FortiOS Carrier and MMS duplicate messages and message floods”.

You can customize the MM4_forward.res message by editing the MM4 duplicate message MM4 replacement message (from the CLI the mm4-dupe replacement message). You can customize the response status and message text for this message. The default response status is “Content not accepted” (err-content-not-accept). To hide the fact that the FortiOS Carrier unit is responding to a duplicate message, you can change the response status to “Success”. The default message text informs the sender that the message was blocked. You could change this to something more generic.

For example, the following command sets the submission confirmation response status to “Success” and changes the message text to “Message Forwarded OK”: