I'm 100% sure. Windows Event Viewer log file can also be saved as a .MTA
Scrap my last comment. As I have looked deeper into this issue .MTA in ETS2MP means
Message Transfer Agent
MTA files associated with server message transfers may contain important information for your computer. If you use any sort of server with your computer, the MTA files are most likely legitimate message transfers that will not cause any harm to your system. These files are relatively small, so it is best to leave them on your computer unless you are certain that deleting them will not harm the server interaction.