Mailing Supply is a term used to describe the materials needed for sending out mail, such as labels, envelopes, and stamps. Labels, which are six letters long, are an important part of the mailing supply, as they are used to identify the sender and recipient of the mail. Labels can be printed or handwritten, and come in a variety of sizes and colors. They are often used to add a personal touch to mailings, and can be used to create a professional look.