Last winter, someone hit my roadside mailbox and broke the post in half, and the box was crushed. My cousin was nice enough to replace it for me. He even got the post and mailbox himself, so I didn't have to do it. Unfortunately, he didn't ask me what kind of box I wanted and just bought a standard size. My previous mailbox was over-sized, so larger packages would fit in it. I didn't say anything about the smaller size box because he was kind enough to do it for me. The smaller size box does inconvenience my postal lady occasionally.
If a package won't fit in my mailbox, she pulls into the driveway and deposits it at my door, along with my mail. I know that mailmen are always pressed for time and want to take as few steps as possible when making deliveries. Some are too lazy to deliver packages that won't properly fit in the mailbox to the door. So it's no wonder they try to jam parcels into mailboxes that are too small.
You could try calling the post office and complaining about your mailbox being damaged from packages being forced in, but that might end up causing you more problems. If you p*ss off your carrier, your mail could end up getting "lost". Or you might consider installing a larger mailbox. Of course, that's not a guarantee that it will stop the mailman from trying to shove packages in any way.
Anyone who gets their mail or packages delivered to their door and is worried about theft could get a locking parcel drop box made from plastic or metal, but larger ones can be expensive. If you're concerned that thieves could run off with the whole box, you can secure it by filling the false bottom with rocks, sand, or other heavy material to make it crazy heavy, or you can drill through the bottom and secure it to the floor.
That's not an option for you, Em, because you have roadside delivery. Maybe a locked parcel drop box that could be cemented into the ground where your mailbox is? It seems like that would be a lot of trouble and expense, but it might help solve your problem. I dunno. You'd have to look into it to make sure it's legal and that the drop box you choose is approved by the post office. I'm just trying to come up with some kind of solution to mail theft and damage. It would probably still p*ss off the mailman because he'd have to get out of the truck every day to open the box.
When we first bought our house, there was no mail delivery. We had to go to the post office to pick up our mail. It was a bit inconvenient but, thankfully, the post office was just a couple of minutes down the road. At least we didn't have to worry about mail or packages being stolen or the mailbox being plowed down.
https://www.amazon.com/Best-Sellers-Package-Drop-Boxes-Lockers/zgbs/hi/17572893011
Bella