Our Certified 6x9 Envelopes are the best quality that you will find. Their durabilty make automated inserting certified mail® easier than ever. The inside tint(not displayed in the image) keeps information inside the envelope unviewable from the outside. In addition to the delivery address window, a second custom window allows the required OCR article number to show through & the third window eliminates the need to print your return address on the envelope. Again, these Certified Mail® envelopes eliminate matching, maintain optimal quality control and are compatible with high volume machines.