Is it legal to put someone’s mail in their mailbox?
<p>If you printed up a flier and walked around shoving them into people’s mailboxes, that would be illegal because it is misuse of postal systems/property.</p>
<p>But what if someone else’s mail gets delivered to you by mistake? Can you just put it in their mailbox? Can anyone just use mailboxes as long as they are being used rightfully and lawfully, or do you have to be some sort of “Certified Deputy of the Postmaster General”?</p>
<p>I know you can just write “delivered to wrong address” on the envelope, but sometimes it is easier to just bring it a few doors down.</p>
<p>Assume for the sake of the question that the mailbox is on or near a public road (accessible without trespassing).</p>

<p>The specific reason why you can't deliver general fliers in mailboxes is <a href="https://www.law.cornell.edu/uscode/text/18/1725" rel="noreferrer">18 USC 1725</a>, which says</p>
<blockquote>
<p>Whoever knowingly and willfully deposits any mailable matter such as
statements of accounts, circulars, sale bills, or other like matter,
on which no postage has been paid, in any letter box established,
approved, or accepted by the Postal Service for the receipt or
delivery of mail matter on any mail route with intent to avoid payment
of lawful postage thereon, shall for each such offense be fined under
this title.</p>
</blockquote>
<p>Misdirected mail has the requisite postage, therefore you can put it in the mailbox.</p>

<p>Yes, under US law (18 USC 1725) you may place misdirected mail in the mailbox of the person to whom it is addressed. You may also just knock on that person's door and hand it to the addressee.</p>

united-states postal-service