The return address is placed on the upper left-hand corner of the envelope in the return address area. It needs to include the mailer's name, address, city, state and ZIP code. The return address area is located in the upper 33 percent of the envelope and the left-most 50 percent. The address should follow the same format as the delivery address. It must also be placed on the front of the envelope, just like the postage stamp.
If printed, the return address needs to be printed in a eight-point font or larger. The United States Post Office requires that the printed return address be in a sans serif font as well. Dark ink is required, with the address being left-justified to make it easier to read. The type size is reducible to six-point font if the return address is presented in all capital letters.
The return address is mostly optional. Its purpose is to provide the post office with a place to send undeliverable mail. It is required, however, for priority mail, when using precancelled postage and when the sender requests extra services. Many organizations use the return address as a form of advertising though, including company logos, or as a brand by prominently listing the company name.