How To Write The Return Address On A Letter . The city, state and zip code. City or town, followed by the state name and zip code. Is it Important to Put the Return Address on the Envelope or Mail? from www.uspsinfo.com In some cases, your recipient may have an appointed peerage title such as duke or baroness, should that be the case, ensure. Write “not at this address” on the envelope. Put the envelope/package back in the mailbox.