How do you stop someone from using your mailing address?

What about contacting USPS Customer Service, if you live in the US?

Write RETURN TO SENDER on the envelope and mail it back.

Instead of calling the institution, google the Director, and write a real letter (snail mail) to the Director and cc: the person who sent the letters to your address. Therefore, both the Director and the person who sent your letters will be notified. If the person who sent your letters doesn’t care or doesn’t know what to do with the information, the Director will. Just explain that you are concerned that this person is using your address, and this person doesn’t live there, nor have they ever.

The person you spoke to is obviously too stupid to comprehend that it’s not about confirming or denying anything, it’s about this client lying about their address.

From the USPS Customer Service FAQ on this topic

Reporting/Returning misdelivered mail

Despite our best efforts, occasionally mail is mis-delivered, or is delivered to an old location for an individual. If you are receiving mail for the previous resident and do not know their address, simply return the mail piece back to the mailstream (by leaving in a Collection Box® or other mail receptacle) with the notation “Not at this address” marked on the envelope.
Important: If the misdelivered item meets any of the following criteria

The Express Mail service item,
An unknown applicant submits proper ID.
The applicant provides a verifiable point of contact (e.g., place of employment, shelter, charitable institution, or social services office).
Please contact the Delivery Supervisor at your local Post Office facility:
For Express Mail items only, you can obtain the number of the Express Mail Reporting Unit by calling:

1–800-ASK-USPS (1–800-275–8777)

For other misdelivered mail items (such as letters):

If the mailpiece is delivered to the wrong location:

Don’t erase or mark over the information, or write any type of endorsement on the mailpiece.
Place the item back in the mailbox or hand the item back to your mailperson.
If the mailpiece is delivered to the correct location but the recipient on the mailpiece does not reside at the address:

Write“Not at this address” on mailpiece.
Don’t erase or mark over the address.
Provide the mailpiece to your mailperson or drop into a Collection Box receptacle.

Destroying mail that was not intended for you may be prohibited by US laws.

Willfully destroying mail is an act that may be punishable by the Federal Government.

If you have any questions about the legality of doing this, please contact your local law enforcement.

Stick your last name on in your mailbox.
I have also called the post office know once of a person I believed was trying to use our mailbox to have strange mail delivered from another country. They tried coming to my door to claim a package that was delivered and were acting really weird and they said they accidently wrote this address because they lived here before. I told them I had already wrote return to sender and put it in the mail box and notify the post office to never deliver their mail here again. Somehow they also got a hold of my phone number and I was getting calls for them as well. They said they had lived here prior to me 4 years ago but the developement was build 2 years before I moved in.
I also had to disconnect my phone. Its been 2 years and I haven’t gotten any wrong mail since.

About a month ago, I received a letter from the local Legal Aid Society. It was addressed to someone who doesn’t live here, who I never heard of (a man, and I’m a lady). The letter said “we are going to excuse ourselves from representing you, as you did not show up for your last court date, and we have been informed that a warrant has been issued for your arrest” or something like that. I received this letter on a Friday. The first thing I did was call the Sheriff’s to make sure they were not going to break down my door. The guy who answered said no. Then the following week I called the Legal Aid Society, and wrote a letter to the Legal Aid Society and cc’d it to the court, attaching the original letter (xerox copy of original letter to the Court’s letter). I explained that I opened the letter by accident and I want to let them know that not only have I never heard of this person, and I have lived in my house for about 10 years, before I lived here the house was owned by family and this person definitely never lived here then, either. I also suggested that the next time they arrest him, they verify his address. I never heard from anybody since. It upsets me that this criminal is saying he lives here and that apparently, people can get out of jail and not show proof of where they live. I probably shouldn’t have opened the letter, since it was not addressed to me. I probably should have just returned it to sender, but if I never opened it, I would not know what was going on. I am glad I know what’s going on, now.

@jca Thanks for addressing the heart of the matter. Yes, I think this is more an issue of someone deliberately using our mailing address than about misdelivered mail.

Great suggestion about writing the director.

@Pandora and @jca So frustrating. Sorry to hear you’ve had similar problems.

I am not trying to start an argument, I am just curious…

Why not just throw them in the trashcan?

It’s one thing to throw unwanted and misdelivered junk mail in the trash. I expect that it’s technically illegal to do so (when it wasn’t sent to “you” or “occupant” in the first place), but I doubt that it would ever be prosecuted.

Throwing away first class mail is another matter. Though I haven’t heard of any prosecutions for throwing away first class mail misdelivered to your address (whether by design or not), I wouldn’t do it or recommend it. I typically mark the envelope very plainly “Not at this address” or “Moved, no forwarding address” or just re-address it myself and drop it in the box. Or I take it to the neighbors, when I get their mail by accident.