I mail any checks right at the post office. And not in the outside box either–I go into the lobby and use the letter slot.
We don’t mail many checks. Most of the time I will use the outside box at the post office providing there is room for it to be properly deposited and it is only a few hours before the next pickup.
It is routine for us to drive by two local post offices. There are times normally after a holiday I see people trying to force more letters into the outside mailbox. Those would be very easy to steal.