Edited to add: While these aren't clips from personal experience, I got a good laugh out of it because we did have a mail slot in the front door when hubby and I were the Resident Advisors/Managers for the Student Housing. We had a Sheltie at the time who was notorious for shredding anything paper.
Unfortunately several of our students monthly rent checks were shredded by our notorious doggy shredder.
In addition to that, when a student was busted for underage drinking and their illegal alcohol unceremoniously dumped down the drain, they had the tendency to knock on our door at all hours in their drunken irate state and attempt to peer into our townhouse through the mail slot, shouting obscenities and trying to get us to answer our door.
Both inconveniences were conveniently rectified when I constructed a box attached to the door to not only block the view from drunken bloodshot eyes, but also catch the mail to deter the doggy shredder.