Mailing is a broad category. A wide umbrella that covers equipment and solutions for preparing bulk mail jobs. Pieces passing through the mail-stream have a unique set of requirements defined by the USPS to ensure that pieces make their way through the postal sorting system without being lost, damaged, or jammed. Any folded mailed piece is required to have a sticky tab applied to hold the folded piece closed. Pieces that hang open are prone to catch in the USPS sorting conveyance systems. Depending on the type of fold and the thickness of the entire documents, sometimes multiple tabs are required. Within the past two years the USPS has redefined the tabbing requirements.
Address printing is another very important part of the mailing process. Obviously mailed pieces must have an address in order to arrive at their destination but there's much more to the story. When mailing in bulk, it's a general rule that the more sorting you do before giving the job the post office, the lower your per-piece rate will be. Addresses are important, but for bulk processing, the USPS expects to have an intelligent mail barcode on each piece. This barcode contains information about the mailing agent as well as the destination. Mailing software will also place mailed pieces in delivery order so the USPS is not tasked with resequencing the job.