First ...... it was wrong it is was illegal
Second ..... as others have said, perhaps, "you do the crime, you do the time".
However, perhaps there is a "middle of the road" here
What if
1. They were required to repair and replace the mailboxes (a given, no option)
2. They are required to do "community service" (some set number of hours each) AT THE HOMES OF THE PEOPLE WHOSE MAILBOXES WERE DESTROYED. The homeowners choice of jobs. I'm sure there are some jobs that those homeowners would LOVE to have done, free of charge! Grass mowings, weed eating, coop cleaning, etc, etc
Just a thought