If you have less than 3 keys, order a replacement or two from a local locksmith or hardware store. The key taped to the mailbox wall is most important. That can always be accessed by the mail carrier and the problem can be quickly corrected.
If you lose all of your mailbox keys, the problem can still be solved but it’s a little more complicated. The barrel of the lock can be replaced. I plan to order a pack of 4 replacement locks. If you have lost all of your keys or if the lock mechanism is jammed, let me know. Jim Groves has volunteered to teach several of us how to replace the locks. It will need to be done when the mail carrier is present.
The best thing you, as a homeowner, can do is to make sure you always have spare keys in a safe place.
George Babbitt