If you lose your mailbox keys and you're in a single family home, you will need to contact the United States Postal Service on 1 League in Irvine. The cost for a replacement lock is $50.00 and it will take 2-3 days to go through the whole process. You will fill out a form at the USPS, present a photo ID, and a current utility bill. If you have any questions, you can call the post office at (714) 368-3374.