What Bulk and Periodical Mailers Need to Know about the New USPS "Flat Tray" Rule

Postage $aver Software
Effective January 22, 2023, USPS has changed the way "flats" are prepared for Marketing Mail (bulk mail) and Periodical Class mail rates. Mailers are required to use "flat trays" (also called "tubs") instead of sacks to submit flats.

Previously, Marketing Mail mailers have been required to use sacks (or, in some case, letter trays) for flats. Periodical Class mailers have had the option of preparing sacks using either flat trays or sacks, but are no longer allowed to use sacks. (There are some exceptions and a short grace period ... see below.)
Three important warnings:
- For some Marketing Mail flats without barcodes, the new rule can result in a significant postage price increase, due to changes in the minimums required for each price category. The minimums were not changed for Marketing Mail barcoded flats or for Periodical Class flats, so their postage is not affected by the rule change.
- Unlike sacks, flat trays must be strapped shut, so you need to order strapping materials. (NOT provided by USPS.)
- For Periodical Class mailers who are already using flat trays, note that you must now turn the tray lids inside out so that the white side shows instead of the green side. Same goes for Marketing Mail mailers.
What are flats?

A flat is any mail that is rectangular, flexible, and fits at least one of the following requirements, regardless of whether it is a card, envelope, or package:
- its shorter side is more than 6 1/8" but not more than 12"; or,
- its longer side is more than 11 1/2"* but not more than 15"; or,
- for Marketing Mail, its thickness is more than 1/4" but not more than 3/4";
- for Periodical Class, its thickness is more than 1/4" but not more than 1 1/4".
* Every Door Direct Mail flats have a different minimum length, but EDDM is not part of this rule change.
How to arrange your mail in a flat tray:
Place all pieces flat in the tray, not vertically. For most mail, you will still be bundling the mail first with rubber bands. In that case, place the bundles so they lay flat, not vertically.
- If more than one piece can fit side-by-side when placed flat in the bottom of the tray, you should make as many side-by-side stacks as possible (while still keeping all pieces horizontal) to use as much of the tray as possible.
If you are using Postage $aver to prepare your mail, it will ask you how many columns will fit in your tray, so it know how many pieces will fit. It will no longer ask for the maximum weight, as you are required to prepare a full tray before starting a new one to the same destination and sort level, unless the tray weighs more than 70 pounds.
If your bundles curl up into rolls and don't lie flat, please see the next topic below.
- All pieces must have the address side facing up, and must read in the same direction.
- Similarly, when preparing bundles, all pieces must have the address side facing up, and generally must read in the same direction.
However, if your piece has a thick edge (for example, a saddle-stitched booklet) such that the bundle would be much thicker on one end, you can alternate the direction of the pieces within the bundle in as many as four roughly equal groups. Note that you are only changing the horizontal direction the pieces face - all addresses must still all face up.
- All flat trays must be covered with a lid, which you can get from USPS when you pick up your trays. For Marketing Mail and Periodical Class, the lid must be flipped so that the white side is showing. (Periodical Class previously used the green side.) First Class Mail flat trays continue to use the green side as in the past.
- Each covered flat tray must be secured with two plastic straps placed tightly around the width of the tray (the shorter dimension). USPS does not provide the strapping material. Strapping kits are available at commercial office supply companies, like these from Uline or Quill. Unlike letter trays, where local trays are exempted from the strapping requirement, we do not find any exemption in USPS rules for flat trays.
How do I create "columns" if bundling causes my pieces to roll up?
You're not really supposed to have rolled bundles, and that's especially important when using flat trays. Bundles are supposed to lie flat. If the rubber band tension causes the pieces to roll up, use rubber bands that won't do that. Here's what USPS says about bundling flats:
For example, if the tray tag says it's a 3D tray going to 770, and the endorsement line on all of the pieces says 3D 770, then no bundles are used. But if the endorsement lines in one of the bundles in that tray say 5D 77005, then all pieces in the tray must be bundled.
For each tray, Postage $aver figures out whether bundles are used, and shows that on the Mail Preparation Instructions report.
- Bundles must be able to withstand normal transit and handling without breakage or injury to USPS employees
- Bundles must be secured with banding, shrinkwrap, or shrinkwrap plus one or more bands. Banding includes plastic bands, rubber bands, twine/string, and similar material. Use of wire or metal banding is not permitted.
- When one band is used, it must be placed tightly around the girth (narrow dimension).
- Bundles over 1 inch high must be secured with at least two bands or with shrinkwrap. When double banding is used to secure bundles, encircle the length and girth of the bundle at least once. Additional bands may be used if none lies within 1 inch of any bundle edge.
- Banding tension must be sufficient to tighten and depress the edges of the bundle. Loose banding is not allowed.
When twine/string is used to band bundles, the knot(s) must be secure so the banding does not come loose during transit and processing.
For example, if the tray tag says it's a 3D tray going to 770, and the endorsement line on all of the pieces says 3D 770, then no bundles are used. But if the endorsement lines in one of the bundles in that tray say 5D 77005, then all pieces in the tray must be bundled.
For each tray, Postage $aver figures out whether bundles are used, and shows that on the Mail Preparation Instructions report.
Exceptions to the flat trays rule, and grace period:
USPS has provided the following exceptions to the flat tray rule where sacks are still permitted.
For Periodical Class, sacks can still be used for flats when presorted at the following levels:
For Marketing Mail, sacks can still be used for flats when presorted at the following levels:
For Periodical Class, sacks can still be used for flats when presorted at the following levels:
- carrier route, 5-digit scheme carrier route, or 5-digit carrier route;
- 5-digit, when mailed at the post office delivering that zip code (the "DDU");
- 3-digit or SCF, when mailed at the SCF (sectional center facility sorting center).
For Marketing Mail, sacks can still be used for flats when presorted at the following levels:
- carrier route, 5-digit scheme carrier route, or 5-digit carrier route.
"This grace period is to allow the mailers time to modify their operations, adjust their mailing plans, and any other procedures to accommodate this change. It will also allow for receipt of mail already in transit for drop ship at the time of the implementation.
During the grace period, the Postal Service will continue to accept and process this flat volume in sacks, bundles, or flat trays without penalty or assessment. The grace period will expire February 21, 2023. At that time, mailers will be required to be in compliance with the new rules. Mailers are able and encouraged to adopt the new rules as soon as they ready."
New Instruction from USPS - released and then clarified 1/20/23: Mailers who submit electronic documentation using mail.dat or mail.xml files, and who require an extension for use of sacks after January 22, 2023, must complete the spreadsheet posted here. Mailers must complete the Sack Extension Request sheet each week and submit it to PCSC@usps.gov each Friday by 11:59 pm EST with the list of that week's impacted mailings. Here are details on how to modify mail.dat and mail.xml files if you are using the grace period.
Mailers who use the USPS Postal Wizard or paper postage statements will have any necessary postage adjustments made by the Bulk Mail Entry Unit when they submit their mailings, and should not complete the spreadsheet mentioned above.
Because some of the exceptions and the grace period were not announced until early January, shortly before our software revisions were scheduled to be released, Postage $aver Pro and Lite will not support the exceptions or the grace period. The update for the January 22 USPS price increase is based on all Marketing Mail flats and Periodical Class flats being prepared in flat trays, as was originally announced by USPS.During the grace period, the Postal Service will continue to accept and process this flat volume in sacks, bundles, or flat trays without penalty or assessment. The grace period will expire February 21, 2023. At that time, mailers will be required to be in compliance with the new rules. Mailers are able and encouraged to adopt the new rules as soon as they ready."
New Instruction from USPS - released and then clarified 1/20/23: Mailers who submit electronic documentation using mail.dat or mail.xml files, and who require an extension for use of sacks after January 22, 2023, must complete the spreadsheet posted here. Mailers must complete the Sack Extension Request sheet each week and submit it to PCSC@usps.gov each Friday by 11:59 pm EST with the list of that week's impacted mailings. Here are details on how to modify mail.dat and mail.xml files if you are using the grace period.
Mailers who use the USPS Postal Wizard or paper postage statements will have any necessary postage adjustments made by the Bulk Mail Entry Unit when they submit their mailings, and should not complete the spreadsheet mentioned above.
The flat trays rule means higher postage for some nonbarcoded flats:
USPS has changed the minimum number of pieces to earn various pricing levels when preparing Marketing Mail nonbarcoded flats.
Marketing Mail flats are priced based partly on the sort level of the pieces. For nonbarcoded Marketing Mail flats, that means, for example, that a sack of pieces all going to the same 5-digit zip gets a better rate than a sack of pieces just going to the same 3-digit area, ADC area, or mixed. For sacks, the minimum to qualify for its own sack has been 125 pieces or 15 pounds, whichever is lower.
The new USPS rule sets a different minimum for nonbarcoded pieces in flat trays. To qualify for its own tray, a sort level now needs to "fill" the tray, which means it has enough pieces to make an 8" stack.
Some quick math works out that for any piece thinner than 1/16", more than 125 pieces is now necessary to earn the lower rates. For a large card printed on 16 point stock, for example, you would need 500 pieces to one zip (or zip scheme) to get the 5-digit price. If your whole mailing was less than 500 pieces, you'd go from paying 65.3 cents per piece to 92.3 cents per piece!
This change in minimums only applies to Marketing Mail nonbarcoded flats. Marketing Mail barcoded flats are priced based on the sort level of the bundle they are in, not by the sack or tray level. Since bundle sizes are not changing, those rates are calculated just as they have been.
We have asked USPS to look at whether the effect of the change on pricing was intended, and to reconsider, but for now, the rule remains in effect.
Questions? Ask us and we'll do our best to answer.
Marketing Mail flats are priced based partly on the sort level of the pieces. For nonbarcoded Marketing Mail flats, that means, for example, that a sack of pieces all going to the same 5-digit zip gets a better rate than a sack of pieces just going to the same 3-digit area, ADC area, or mixed. For sacks, the minimum to qualify for its own sack has been 125 pieces or 15 pounds, whichever is lower.
The new USPS rule sets a different minimum for nonbarcoded pieces in flat trays. To qualify for its own tray, a sort level now needs to "fill" the tray, which means it has enough pieces to make an 8" stack.
Some quick math works out that for any piece thinner than 1/16", more than 125 pieces is now necessary to earn the lower rates. For a large card printed on 16 point stock, for example, you would need 500 pieces to one zip (or zip scheme) to get the 5-digit price. If your whole mailing was less than 500 pieces, you'd go from paying 65.3 cents per piece to 92.3 cents per piece!
This change in minimums only applies to Marketing Mail nonbarcoded flats. Marketing Mail barcoded flats are priced based on the sort level of the bundle they are in, not by the sack or tray level. Since bundle sizes are not changing, those rates are calculated just as they have been.
We have asked USPS to look at whether the effect of the change on pricing was intended, and to reconsider, but for now, the rule remains in effect.
Questions? Ask us and we'll do our best to answer.
