Postal regulation regarding window envelopes

What does the regulation state?

The revised postal regulation (DMM 601.6.3) states that the delivery address on mail sent in window envelopes must show completely, with 1/8” clearance, at all times during processing and delivery, even if the insert moves.

What is the DMM?

The DMM is the Domestic Mail Manual. It is the USPS manual that contains standards governing domestic mail services; descriptions of the mail classes and services and conditions governing their uses; and standards for rate eligibility and mail preparation.

Does this pertain to my mail?

The regulation pertains to all mail sent in window envelopes.

What is the 'tap-test?'

The “tap-test” is the method used to see if mail meets the regulation. The mail is tapped on the top, bottom, right, and left sides. The delivery address must remain visible in the window with 1/8” clearance at all times.

What will CMS do with my mail to check for compliance?

Mail sent in window envelopes will be subject to the tap-test. Mail that does not meet the regulation will be separated and metered at full-rate (no presort discount applied). All mail will be submitted to the post office without delay.

Will CMS notify me if my mail does not meet the regulation?

No, CMS will be conducting random quality control tests but will no longer be notifying the sender.

Can CMS help us pass the tap-test?

CMS is committed to assisting customers meet this regulation. There are several ways to alter mailings to meet this regulation; changes to the size of the envelope or envelope window, re-formatting of the address, adjustments to the insert fold/size, etc. Call CMS customer service with your specific question at 360-664-9506.

What happens to my mail if it does not meet the regulation?

Mail that does not meet the regulation will be metered at full rate and submitted to the USPS. However, by postal service standards this mail is considered “nonmailable” and may be returned to the sender by the USPS.

How can I find out more?

For specific questions contact CMS at 360-664-9507. Additional information can also be found on the United States Postal Service website at

DMM 601.6.3

The regulation as written in the USPS Domestic Mail Manual:

6.0 Special Mailing Containers

6.3 Window Envelope

For all letter-size and flat-size mail in window envelopes, every character in the delivery address, including any postal barcode, marking, or endorsement, must be completely visible through the window throughout the full range of movement of the insert bearing the delivery address. Any window envelope used for letter-size or flat-size mail claimed at automation rates or for letter-size mail claimed at Enhanced Carrier Route high density or saturation rates must also meet the barcoding standards for letters and flats in 708.4.0. Any window envelope used for letter-size or flat-size mail claimed at any other rate must meet the following additional standards:

  1. The address and any barcode visible through the window must be printed on white paper or paper of a very light color.
  2. A clear space of at least 1/8 inch is required between the address block, which includes any optional endorsement line and any barcode, 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. For non-automation rate mail, the bottom edge of the address window must not extend more than 1/8 inch into the barcode clear zone as defined in 202.5.1. Any letter-size envelope containing a window that intrudes into the barcode clear zone is not eligible for MLOCR or RVE FASTforward processing options for the Move Update standard in 233.3.5.
  3. Window cover material, if used over the address window, must be made of a non-tinted clear or transparent material (e.g., cellophane or polystyrene) and must permit the address, as viewed through the window material, to meet the print-contrast ratio standards in 708.4.0 to ensure efficient processing and delivery. Glassine may be used for window cover material. All edges of the window cover material must be glued securely to the envelope. The bottom edge of an address window must be at least 1/2 inch from the bottom edge of the envelope.
  4. For letter-size mail, the delivery address window must be parallel with the longest edge of the envelope. For flat-size mail, the address window may be parallel with any edge of the envelope.
  5. For Registered Mail, the opening on a window envelope must be covered as described in 503.2.4.8.