Had a problem at a previous apartment with people breaking into the physical mailbox and stealing credit cards, then activating and using them for a day before I caught it. Happened a few times to my and a few times to another resident that I talked to about it. Apartment complex is huge (~35 buildings with ~30 units per building) and owned by an even bigger company with dozens of properties around the country. Got the actual mail fraud investigator people to come out and yell at the apartment management about having an improperly-secured mailbox after my talking to them had no effect. The mailboxes were wall-mount indoor units where one big swing-open panel gave access to ~40 mailboxes; the locking mechanism was just a padlock and a slider bar. The slider bar was mounted to drywall with drywall anchors, so to break in, they used a claw hammer or crowbar to just rip the locking mechanism out of the wall, left the door open, threw ripped-open mail everywhere... the apartment maintenance people just filled the holes with drywall filler,
then put the drywall anchors back into that. You could pull it out with your fingers, and it looks like that was exactly what happened on subsequent thefts.
Anyway, the apartment management people basically told the USPS inspectors “new mailboxes cost money” and that was that. I moved out a few months later and mentioned that this incident was partially the cause. USPS recommended that I use a post office box to ensure that my mail wouldn’t get stolen, which I understand, but at the same time is pretty ridiculous IMO.
TL;DR USPS was very responsive and sympathetic to my situation, but ultimately couldn’t actually make my huge apartment company secure their mailboxes.