Letter size mailpieces prepared for automation which are not in an envelope must be tabbed (or wafer sealed) to prevent an open edge from catching in postal processing equipment. The bottom edge must be the final fold in all cases except when using an oblong design with the final fold on the right.
The mailpiece must be tabbed with non-perforated 1 ½” tabs.
Specifications for Automation-Compatible Letter-Size Mailpieces:
Flat size mailpieces do not require wafer seals. However, they can be added to ensure the integrity of the mailpiece as it is
processed through the USPS.