Take the right steps.

The U.S. Post Office delivers an astonishing 506.4 million letters and packages every single day and most of them end up in the right place. Occasionally, though, they do make mistakes and someone else's mail ends up in your mailbox. It could be that the mail is addressed to a former resident, the letter was slipped into the mailbox of apartment 2C instead of 2E, or perhaps the mail carrier simply delivered a letter intended for 360 Main Street to 360 Main Avenue. Whatever the reason, mail does occasionally end up in the wrong mailbox and the question about what to do with it falls to the recipient.

The first rule of handling someone else's mail, is to treat it as you would hope someone would treat your own. Don't open it and try to keep it in good shape while you focus on getting the mail into the right hands.

The easiest solution, if you have the time and mobility, is to consider delivering the misdirected mail yourself. If the person lives nearby or just down the hall, you can either slip it in their mailbox or, if you can't open their mailbox without a key, consider* gasp!*  knocking on their door. If they are at home, you can hand over their mail and meet one of your neighbors at the same time.

If the mail is intended for someone who lives too far away to hand deliver, or you simply don't have the time to take on the uninvited task, simply place the item back in the mailbox for your mail carrier to pick up and deliver correctly. In her column in the Houston Chronicle, Heloise notes that there's no need to mark on the misdelivered item. Instead, simply return it to the mailbox and hope the mail carrier gets the hint or perhaps affix an explanatory note on a Post-It. That said, KOMO News suggests that if one of those stick-on barcodes has been attached, scribble it out or peel-off the sticker or else you risk getting the card returned to you in the next day or two.

If you're receiving mail for a person who no longer lives at the address, write "not at this address" on a note attached to the misdirected mail. If the problem persists, contact the post office either on the phone or in person and alert them to the situation. As Lifehacker points out, though, keep an eye out for mailing addresses that include the phrase "or current resident," as that mail is technically addressed to whoever happens to live in the house at the time and if that's you, it's yours to do with as you wish.

If receiving the incorrect mail in your mailbox is a persistent problem, call the USPS Consumer Affairs office and file a complaint, or report it to your local postmaster.