If you are currently using window envelopes for your mail, there are several things you must keep in mind: 

First, the address must show through the window with a 1/8 inch margin throughout the full range of motion of the insert.  While the previous USPS attitude had been that if we had a readable barcode in the Barcode Clear Zone, the address shifting out of the window was irrelevant, current verification proceedures (including Move Update verification) necessitate that the USPS be able to read the address.  As a result, some Business Mail Acceptance Units in the country have begun performing "Tap Tests" on mailings containing window envelopes.  Since the USPS regulation that dictates address visibility in window envelopes (DMM 601.6.3) is in the Mailability section of the DMM, failing to meet the shift requirement means a mailpiece, and any mailing that includes such a mailpiece, is unmailable.  This diagram is an example of unacceptable address shift.

 Also, while the industry standard window position on an envelope has been a half inch up from the bottom, the USPS reserves the bottom 5/8 inch of the envelope as the Barcode Clear Zone.  This means that a standard window violates this Clear Zone.  The USPS specifically states that envelopes with windows that encroach the Barcode Clear Zone are not elegible to use FASTforward as their method of Move Update (DMM 601.6.3b).

Please keep these in mind when mailing with Window envelopes.  Post Masters asks our customers to make sure they when they reorder window envelopes, they make sure the get windows that are at least 5/8 of an inch up from the bottom of the envelope.

For more information, refer to http://pe.usps.gov/text/dmm300/601.htm#wp1064805 or contact Post Masters.