Presort uses the term ‘fletters’ to describe the area of overlap between the USPS height and width limits for regular letters, and the limits on automtion flats. You will not find the term ‘fletter’ in the USPS DMM.
A ‘fletter’ is a mail piece whose dimensions qualify it as an automated flat or a regular letter.
When you presort fletters, you can save on postage by processing the pieces with a 9-digit ZIP Code as automated flats and the remaining pieces as regular letters. (The automated flats get a better postage rate.) For Periodicals and Standard Mail only – you are given the choice to prepare the non-automation pieces as letters or flats. You can choose to process all pieces as flats to save on production costs.
If you choose to process the entire mailing as flats, the non-automation pieces are charged flats rates, resulting in higher postage rates but reducing production time and labor costs. Choose which benefits you the most.
When setting up the job in order to get the automated flat rate, if the height is 5.375 to 5.999 inches, enter the value at the Width parameter. Enter the width of the mail piece at the height parameter. Essentially reverse the orientation of the mail piece when measuring its dimensions.
In COMAIL fletters all pieces are prepared as flats under the exceptions provided for within the DMM.
The USPS requires that you co-bundle fletters when they are not palletized. You must enter Yes into the Co-Package and Auto and Reg Pieces parameter in the PER, Flats scheme. The software does not warn you if you do not have this setup correctly.