What is what to do with mail that is not yours?

Dealing with mail not addressed to you depends on what kind of mail it is and how it got to your address. Here's a breakdown:

1. First Class Mail (letters, postcards):

Clearly Misaddressed: If the address is clearly wrong (wrong street number, wrong city, etc.), write "Not at this address" or "Return to Sender" on the envelope and place it back in your mailbox for the postal service to pick up. You can also add the correct address if you know it.
Slightly Misaddressed (but obviously not yours): Same as above – return to sender.
Address is Correct, but not your name: This is trickier. If it's a first-class letter, it's likely sensitive personal information. Do NOT open it. Write "Not at this address" or "Return to Sender" and put it back in the mailbox.

2. Standard Mail (junk mail, magazines, marketing materials):

Clearly Misaddressed: You can discard it.
Slightly Misaddressed or Correct Address, Wrong Name: You can usually discard it. However, if it contains a return address, you might consider marking "Return to Sender" and placing it in your mailbox. This is less crucial than with first-class mail.

3. Packages:

Clearly Misaddressed: Refuse the package. If the carrier leaves it, you can often write "Return to Sender" on the package and leave it where they left it or take it to the post office for return.
Correct Address, Wrong Name: This is more problematic. Don't open it! Contact the shipping carrier (UPS, FedEx, USPS) using the tracking number (if available) to inform them of the misdelivery. They'll handle getting it to the correct recipient. You may need to refuse it if they can't immediately retrieve it.

Important Considerations:

Never open mail that is not addressed to you, except in very limited circumstances (such as a clearly misaddressed piece of junk mail). Opening someone else's mail is a federal crime.
Be careful with forwarding mail. Only forward mail to people you know and trust. Forwarding other people's mail is illegal.
If you consistently receive mail for someone else, inform the Post Office. They may be able to update their address information to prevent future misdeliveries.
If you suspect mail fraud or identity theft, contact your local authorities and the appropriate agencies (like the FTC).

By following these guidelines, you can ensure you're handling misdelivered mail properly and avoid any legal or security issues.