The term POST OFFICE ITEM can be broken down into two crossword solutions: MAILER (6 letters) and STAMP (5 letters). A MAILER is an envelope or package used to send items through the post office. It is usually made of paper, cardboard, or plastic and is designed to protect the item inside. A STAMP is a small adhesive paper that is affixed to a letter or package to indicate that postage has been paid. Stamps are typically issued by a government postal service and come in various denominations. Together, a MAILER and a STAMP are essential items for sending items through the post office.