Problems with USPS/mail carrier!?

I have received the exact same letter now, three times, addressed to someone not in my household, and not even my house number. This is the fault of the United States Postal Service.
I keep writing on the envelope that this person is not at our address and then I drop it back off at the post office's blue mailbox. Like I stated, this has happened three times now with the exact same envelope. I am in the process of filing a complaint with my mail carrier, as there have been several other problems I've experienced with him.
I finally emailed the sender, that this letter has not reached the person it was intended for. I could assume that the USPS keeps delivering it to me because we share the same last name, but "*****" is fairly common, so I really hope the post office hasn't become this ignorant.
I really feel like I can't trust my mail carrier anymore. There have also been several mail parcels that I expected but never received over the past few months.
What should I do?

There haven't been any barcodes imprinted on the envelope. After the first time I dropped it off, they stamped it with a "RETURN TO STA._________ FOR CARRIER MARK OFF." And it just keeps coming to me like that.

Simple solution...
DO NOT drop the letter in the blue collection box.
DO NOT write on mail that is not addressed to you, that is against postal regulations.
Hand the letter to your letter carrier, and verbally tell him of the problem.

The USPS has a system in place called DPS. (Delivery Point Sequencing). The letter has been sorted by a machine to your address, with the machine imprinting a barcode on the front and back of the envelope. If you throw the letter in the blue collection box, it has entered the mailstream again. The sorting equipment will always read that barcode, even if you wrote on the envelope
Mr. John Smith
1313 Main St.
Planet Venus
It will not read the writing once a barcode is placed on it.

In some post offices, Letter carriers are instructed NOT to visually check every piece of mail that they deliver. Therefore they may be skipping over that item if you have numerous pieces of mail. So they may be unaware of the merry-go-round that the letter is on. That is why you should HAND it to the carrier.
That should solve the problem.

You really need to check with your local post office. When you knew a package was scheduled to arrive and it didn't, you should have handled that problem at that time instead of waiting for this all to culminate and then report it as a problem.

As far as that envelope, just throw it out if it comes again.

Drop the letter at the right house,, I bet the person gets some of your mail too! Then get yourself a PO BOX!

I always just put wrong address and put it back in the mailbox with the flag up. This way the mail carrier will see that it is not yours and will take it to who it belongs to. If you drop it off at the post office it just gets rerouted to him again and he drops it in the same box because the last place he took it to was the wrong address not realizing he is dropping it in the same place. If that doesn't work just go knock your mailbox over and do everything online. And use Ups for receiving big packages.

Go to your local post office and make a complaint. If you are lucky, he will get fired and replaced with someone who is better.