Properly writing the return address on an envelope ensures that if the recipient can't receive it, you get it back with an explanation from the post office. Although not required on most first-class mail, the U.S. Postal Service strongly recommends you always put a return address in case the mail gets misdirected or damaged. The USPS requires a return address on some types of mail such as Express Mail, and knowing the proper procedures helps you get your items on their way without delay.
What to Include
A return address should include enough information to ensure the letter can be returned to you efficiently. It needs the same information as the delivery address, including your name, your address with apartment or suite number if applicable, and your city, state and ZIP code. Use a printed address label or a blue or black pen. Business envelopes might include the company's logo beside the return address as well.
The U.S. Postal Service prefers the return address in the upper left corner of the envelope. When you address the envelope, turn it so the longest sides are along the top and bottom. The return address goes top left, the stamp goes in the top right corner, and the delivery address sits in the center.
Large Letters and Packages
When dealing with large envelopes and packages, you might prefer to use an address label. The post office provides labels for services such as Priority Mail and Express mail. These labels include spaces for the return address and the delivery address. Treat these labels like an envelope, with the return address in the upper left corner of the label and the delivery address in the center.
Traditionally, etiquette allows the return address to sit on the flap of the envelope rather than printing it on the same side as the delivery address when mailing formal invitations to events such as weddings or graduations. However, the post office strongly encourages you to place the return address on the same side as the delivery address to make the return process seamless if it becomes necessary.