For Registered Mail pieces, the opening on a window envelope must be covered as described in DMM 503.2.3.5.I am not familiar with the standard letter class.For flat-size mail, the address window may be parallel with any edge of the envelope. For letter-size mail, the delivery address window must be parallel with the longest edge of the envelope.The bottom edge of an address window must be at least 1/2' (5/8' preferred) from the bottom edge of the envelope. All edges of the window cover material must be glued securely to the envelope. Glassine may be used for window cover material. Window cover material, if used over the address window, must be a non-tinted clear or transparent material (e.g., cellophane, polystyrene) and must permit the address, as viewed through the window material, to meet the print contrast ratio (PCR) standards in DMM 204.1.4 to ensure efficient processing and delivery.Any letter-size envelope containing a window that intrudes into the barcode clear zone is not eligible for NCOA Link mail processing equipment system processing for the MOVE Update standard. For nonautomation price mail, the bottom edge of the address window must not extend more than 1/8' into the barcode clear zone as defined in DMM 202.5.3d. See DMM 202.5.1 (letters) or 202.5.2 (flats) for barcode clearances when the address block contains a barcode.

A clear space of at least 1/8' is required between the address block, which includes any optional endorsement line, and the top, bottom, and left and right edges of the address window, and must remain when the insert is moved to its full limits in each direction within the envelope to ensure efficient processing and delivery.

The address and any Intelligent Mail barcode visible through the window must be printed on white paper or paper of a very light color.

Any window envelope used for letter-size or flat-size mail must meet the following additional standards: Any window envelope used for letter-size or flat-size mail claimed at automation prices, or for letter-size mail claimed at Enhanced Carrier Route High-Density or Saturation letter prices, must meet the barcoding standards for letters. For all letter-size mail in window envelopes, every character in the delivery address, including any Intelligent Mail barcode, marking, or endorsement, must be completely visible through the window throughout the full range of movement of the insert bearing the delivery address.

Envelope address window template