Flats Sequencing System

The USPS® is deploying a new technology that will boost efficiencies in the processing, distribution, and delivery of flats–the Flats Sequencing System (FSS). FSS will automatically sort flat-sized mail into delivery point sequence at high speeds. The efficiencies gained by employing FSS are influencing many changes within both the Postal Service® and the mailing industry.

Who is Flats Sequencing System for?





Standard Mail

Standard Mail

Mail Preparation


Mailers preparing machinable flat-sized mailings must now use FSS Scheme Bundles. These bundles contain all of the mail for a single sort scheme on one of the FSS machines. Usually, this is all mailpieces addressed to one or more 5-digit zip codes.

Benefits to Mailers

These scheme bundles replace previous sorts that separated flats into bundles specific to each carrier. This results in fewer total bundles, which may represent significant savings in the postage for some types of mailings, such as periodicals. In addition, you may be able to simplify production costs associated with preparing bundles.

  • Fewer bundles
  • Potentially reduced postage
  • Potentially reduced production costs

Featured Resources

Flats Sequencing Systems FAQs

Commonly asThis document provides frequently asked questions (FAQs) and answers to Flats Sequencing Systems, the latest generation of mail-sortation that automates the sorting of flat-sized pieces. 

Flats Sequencing Systems (FSS) Locations Map

This document provides the FSS locations map.

Flats Addressing Resources

Effective March 29, 2009, new address placement and formatting requirements adopted by the Postal Service® for Periodicals, Standard Mail®, Bound Printed Matter, Media Mail®, and Library Mail flat-size pieces sent at automation, presorted, or carrier route prices, will be implemented. USPS® also adopts related revisions for automation and presorted First-Class Mail® flats.

Fact Sheets
New Address Requirements for Automation, Presorted, and Carrier Route Flat-Size Mail

The Postal Service adopts new address placement and formatting requirements for Periodicals, Standard Mail®, Bound Printed Matter, Media Mail®, and Library Mail flat-size pieces sent at automation, presorted, or carrier route prices. 

Fact Sheets
Addressing Fact Sheet for First-Class Flats

This document is for mailers who are sending flat-size mail (such as large envelopes) at Automation and Presorted First-Class Mail prices.

Addressing Fact Sheet for Periodicals Flats

An overview of new address requirements for mailers who are sending flat-size Periodicals (such as magazines and newspapers).

Fact Sheets
Addressing Fact Sheet for USPS Marketing Mail Flats

This document is for business mailers who are sending flat-size USPS Marketing Mail (such as large envelopes, catalogs, and circulars). To use the USPS Marketing Mail prices, you must send at least 200 pieces or 50 pounds of mail at a time, prepared and sorted according to Postal Service guidelines.

Fact Sheets
Addressing Fact Sheet for Package Services

This document is for mailers who are sending Flat-size Bound Printed Matter (such as catalogs) using the Presorted or Carrier Route prices or Flat-size Media Mail or Library Mail (such as large envelopes) using the Presorted prices.

New Address Standards for Commercial Flat-Size Mail Presentation

This presentation outlines the standards for commercial flat-size mail including address characteristics and placement, Federal register overview, mailpiece examples, and FAQ's.

Fact Sheets
New Address Standards for Flat-Size Mail Poster

New address placement standards apply to all Periodicals, Standard Mail, and Package Services flats mailed at presort, carrier route, and automation prices (optional for First-Class Mail). This document provides detailed information on address placement.

FSS Deployment Information

This section contains the most current FSS deployment information including: FSS locations, deployment schedules, operational sites, and FSS zones.

Related Products

Labeling Lists

The Labeling Lists Data Product assists mailers with presorting mail by providing active, originating 3- and 5-digit ZIP Code™ data, along with their destination locations, for labeling purposes.