I made the mistake of mailing a Money Order to DC. Yep. Went postal on me and never showed up.
The machines at the PO scans the letters quicker than you can blink, some get caught up and mangled at times. You will never see that mailing again and they don't care.
I worked at the PO at one time, I also have two checks each over $500 somewhere mangled in the PO trash, been out there for about 10 yrs now. No, I did not stop payment on the checks, I knew what happened.