Probably none. They leave mail unattended in mailboxes all over the country.
Weight of the US Marshals keeps it safe - except from a joy rider that likes to drive about and toss mail because he hates the environment and the “Man” and our government......fantasy, sorry. Just don’t tempt me, again.
if the mails properly once the mail leaves “their hands”..its “out of their hands”..so to speak.