What does it mean that your mailers are USPS approved for auto-mailing?

Information Packaging has had our 1-Way and 2-Way MailSaver® tested and approved by the Engineering Department of the United States Postal Service for processing on letter-size automation equipment. These mail pieces can be processed by the USPS without surcharges or additional fees typically incurred when mailing one CD or DVD in our mailers. When properly prepared and sealed, our CD mailers are in the shape of a rectangle. This helps in two ways: the CD is centered in the mailer, providing extra protection on the sides of the mailer. Additionally, rectangle mailers cost less to mail than square mailers.

What does it mean that your mailers are USPS approved for auto-mailing?