Dancy Weatherproof Wall-Mount Locking Ranch Mailbox with

Locking Mailbox, Weatherproof Galvanized Steel Cover Metal Drop Box, Secure Mail Box with Key Lock, Outdoor Dropbox with Slot for Envelope, Home, Office

DEAYOU Wall Mount Mailbox, Steel Cover Metal Drop Box, Mail Box with Key Lock, Dropbox with Slot for Envelope, Home, Office Business, Decor, Black Wall Mount

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mailbox with slot and lock tl;dr: Adding a lock yourself may not be legal, but you can buy a USPS-approved mailbox with a lock The box will need a mail slot or similar,