How do Secure Locking Mailboxes work? - The Basics

How Do Locking Mailboxes Work?

When first considering a secure locking mailbox, people ask questions like:

  • “Does the mail carrier need a key?”
  • “Is my outgoing mail secure?”
  • “Why does a locking mailbox need a flag?”

This article answers all those questions and more.  We cover the basics that you need to know about secure locking mailboxes and how they work. 


A locking mailbox protects your INCOMING mail.  The postal carrier does not have a key. The mail person deposits your mail in a slot or hopper (two different incoming mail styles).  

The United States Postal Service (USPS) specifies minimum slot size for incoming mail.  Manufacturers can make slots bigger.  The important feature for you to consider is whether the slot is too big.  Bigger slot design makes it easier for a thief to reach their hand in and “phish” your mail out. Make sure the mailbox you buy is the right size to deter a thief, yet big enough to accept small packages.  Make a note of the typical package sizes you normally receive. If you often get larger stacks of mail or small packages, then a hopper style is a better option.

Mailboxes with “hoppers” can usually accept larger bundles of mail and packages.  The hopper design should allow the back edge of the hopper to swing almost flush with the inside wall of mailbox.  A well-built hopper tends to be more secure.

Your INCOMING mail stays locked in the mailbox bottom.  You will use your key to open the retrieval door to collect your mail.


Outgoing mail is unsecured – NOT locked.  Steeltech Mailboxes protect your outgoing mail from the elements. The outgoing mail is held on to side of the hopper door with a tight clip. But the outgoing mail is NOT locked.

We recommend you do not put sensitive outgoing mail in your roadside mailbox.  Sensitive mail includes: checks for bills, utilities and credit cards. Documents with personal identifiers like school records, legal or health documents and medication orders are unsafe to remain in the outgoing mail clip. Anything waiting for pickup by the mail carrier is vulnerable.  A letter to grandma is probably Ok.   

When using your outgoing mail feature, put the red flag up.  This lets the mail carrier know he/she needs to stop and pick up your mail.  After collecting your mail, they’ll put the flag back down.  The red flag is a signal to your carrier but can also be a signal to thieves.

Your other options for sending outgoing sensitive mail are:

  • Stop at post office and deposit your mail in the inside depository
  • Deposit outgoing mail in an official blue USPS mailbox
  • Wait curbside and hand mail directly to your carrier
  • Have a trusted family member or friend do any of the above

If you have more questions about locking mailboxes, or you’re wondering which size best fits your needs, call or email Steeltech Mailboxes.

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