What I would do is open every file I could find that relates to mms on the device. Then use a search function to find "agent". Always make a back up of the original file before editing and if you export the file to windows make sure you use an editor that will retain linux permissions.

Idk what the actual program name is but since it is integrated in conversations (is it even called that in harmattan?) it may not even be called mms ...the actual name for conversations in fremantle is rtcom-messaging.