I'm asking about the advice to "just buy a lock for your mailbox" from Neighbor examines (but does not take) mail in my mailbox. (Note: The question and my own experiences are about the US, but the answer is about Australia.)

I can't say I know too much about the subject, but I know the USPS regulates what mailboxes can be used. I've seen cluster mailboxes (like my own condo's) which come with locks, and online I could buy a mailbox (the traditional type, for a regular house) with a lock, but I've never seen or heard of installing a lock on a mailbox without one.

Is putting a lock on your mailbox legal? If so, are there any restrictions on how to do it?

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    You have to let the letter carrier put the mail in the box. Commented Feb 16 at 3:52
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    I presume you have a specific jurisdiction in mind. I could answer for Germany, for instance, but that would likely not help you -- but perhaps other readers of this site.
    – o.m.
    Commented Feb 16 at 6:42
  • @DavidSmith Do you really have to? What if your mailbox is just a rustiy piece of ... that cannot be opened after a while? Would someone come arrest you? That would be worth an answer for that juristiction.
    – nvoigt
    Commented Feb 16 at 7:00
  • I do not feel comfortable writing a comprehensive answer for the US, but I have been there and at least in the big city I have been to, they had the same mailboxes as we have back in Europe, that can only be opened with a key. So if it is illegal to lock a mailbox in the US, that must be based on very specific state laws that don't apply on national level (or I just happened to live in the "rogue mail city" where everyone breaks the law).
    – nvoigt
    Commented Feb 16 at 7:08
  • @nvoigt Mail boxes are regulated by Federal law as part of delivering the mail. If the letter carrier can't put the mail in the box then they don't deliver it. They might leave a message to that effect. Commented Feb 16 at 19:40

2 Answers 2



in fact it is the default and explicitely mentioned in laws as "specially secured against disclosure by a sealed container".

A household mailbox normally has a way (normally a covered slit) to put in mail, but the only access to take the mail out without technical means is a door that is locked. Although steel, it mostly is flimsy and can be forced by a 12 year old with a screwdriver, but it is a pretty clear line of "now you are doing something illegal" that everyone understands.

In case someone wonders, in Germany, we don't send mail through our personal mailboxes. Sending mail is done by putting it into a public mailbox that gets emptied and send every few hours or a post office.

See Can your neighbor search your mailbox? and Neighbor examines (but does not take) mail in my mailbox.

Slight detour:

I don't think that it was the intend of the original phrase, but just in case we are talking about taking that phrase completely out of context: What if you actually really lock your mailbox. So it cannot receive mail either? Well, you won't receive mail then. The mailman will leave a note pinned to your door, where and when you can collect your mail. Any mail will count as having been delivered. If you don't collect it, and potentially miss deadlines or court hearings that is your problem.

§ 179 Zustellung bei verweigerter Annahme

  1. Wird die Annahme des zuzustellenden Schriftstücks unberechtigt verweigert, so ist das Schriftstück in der Wohnung oder in dem Geschäftsraum zurückzulassen.
  2. Hat der Zustellungsadressat keine Wohnung oder ist kein Geschäftsraum vorhanden, ist das zuzustellende Schriftstück zurückzusenden.
  3. Mit der Annahmeverweigerung gilt das Schriftstück als zugestellt.


§ Section 179 Service in the event of refusal of acceptance

  1. if acceptance of the document to be served is refused without justification, the document must be left at the residence or business premises.
  2. if the addressee has no home or business premises, the document to be served must be returned.
  3. upon refusal of acceptance, the document shall be deemed to have been served.

However, even then, it certainly is to your disadvantage to actually bolt your mailbox shut so you cannot receive mail, but it is still not illegal.

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    Bolting shut mailboxes is typical for houses or flats that are abandoned - together with a note that the recipient is not there, putting such mailboxes under §179(2)
    – Trish
    Commented Feb 16 at 13:22

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, so delivery is possible without unlocking.

There does not appear to be some overriding federal law governing mailboxes, so there may be state-specific regulations. However, I would assume that the rules set by the United States Postal Service (USPS) are more or less valid in all states.

According to the USPS (emphasis mine):

Curbside mailboxes - Installation policies

Installation of curbside mailboxes must meet specific construction standards, which can be obtained from the local Post Office™ facility.


The following are a few of the regulations that apply when installing a curbside mailbox:

Important: Before installing, moving or replacing your mailbox or mailbox support, you will need to contact your Postmaster or mailperson from your local Post Office™.

All mailboxes must be approved by the Postal Service™.

Requirements for city delivery mail receptacles

So, from reading the page it seems that you may not alter your mailbox by adding a lock.

You must either:

  • buy a mailbox that is approved by the USPS, or
  • seek approval from the USPS for your mailbox with your own lock

Of course it is possible that a lock on your mailbox will be tolerated in practice, but that appears to be the official situation.

Note that approved, locking mailboxes are available - for example, wall-mounted mailboxes usually have a lock. You could install one of these. A web search for "usps approved wall mailbox" finds many options.

This is further clarified by this FAQ (emphasis mine):

Locked Mailboxes


If you would like to obtain a locked mailbox for your residence:

  • you may purchase one at a local store
  • you may purchase one online from an approved manufacturer

Note: A mailbox with a lock must have a slot that is large enough to accommodate your daily mail volume. The Postal Service™ neither opens a locked box nor accepts a key for this purpose.

Locked Mailboxes and Mailbox Keys

This also explicitly mentions that while there may be a lock to prevent taking out mail, it must still be possible to deliver mail without opening the lock.

Also note that there is an explicit prohibition by the UPSPS on "locked mailboxes" - however, that refers to boxes that must be unlocked for delivery - these are prohibited by Postal Operations Manual 632.527:

The use of locks, locking devices, or inserts on curbside mailboxes on rural and highway contract routes is prohibited. See the list of curbside mailbox manufacturers for approved locking style mailboxes (a current listing of approved manufacturers and models can be obtained from the office listed in section 632.511). The Postal Service does not allow carriers to open locked boxes and does not accept keys for this purpose.

Finally, note that the USPS distinguishes between a personal mailbox and a cluster box (or cluster box unit, CBU). A personal mailbox is the usual mailbox for a single household, while a cluster box is meant to hold the mail for multiple households. Cluster boxes usually installed for all residences in a neighboorhood or in an apartment building. Some rules are different for CBUs - for example, they may be allowed to require a lock for delivery.Thanks Brian for pointing this out.

  • If you add a lock to your existing approved mailbox, does it become an illegal unapproved mailbox, or do you then just have an irrelevant structure and no approved mailbox?
    – interfect
    Commented Feb 16 at 14:54
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    Note that this answer is citing the regulations for home mailboxes. Cluster mailboxes (described in the same document) are permitted to require unlocking for delivery. Of course, probably all the cluster mailboxes on a route will be keyed the same (or will use keyboxes that are keyed the same), so this isn't super secure.
    – Brian
    Commented Feb 16 at 21:58
  • @Brian: Thanks for the remark; I put it into my answer.
    – sleske
    Commented Feb 19 at 8:28

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