USPS does not publish a page of rejection reasons, so this list is built from its rules: if a mailing breaks one of them, the Post Office can refuse it, hold it or charge a different price. Each row names the rule and where it is written.
| Mistake | The rule | How to avoid it |
|---|---|---|
| A piece that is not a flat | Must weigh 3.3 oz or less and exceed 10½″ long, 6⅛″ high or ¼″ thick (DMM 143.2.5). Non-flats are parcels paying parcel prices. | Check the size before you print. Size rules. |
| Postage mark in the wrong place, or missing | The indicia goes above and to the right of the address, larger than 0.5″ × 0.5″ (USPS EDDM page). | Reserve the top-right of the address side on your artwork. |
| Bundles the wrong size, or no facing slip | Bundles of 50 to 100 pieces with a facing slip on top, showing the count, and no taller than 6 inches. | Bundle by carrier route using the counts from the USPS EDDM tool. |
| Mixing routes in a bundle | Flats are separated by delivery route using the tool’s delivery statistics. | One route per bundle, with the piece count written on its facing slip. The route information goes on the back of PS Form 3587. |
| Too few or too many pieces | 200 minimum and 5,000 per ZIP Code per day. | Split a big mailing across days or ZIP Codes, or use BMEU. |
| Dropping at the wrong Post Office | Entered at the Post Office responsible for the routes. | One drop per delivering Post Office. The tool lists them. |
| Missing or incomplete paperwork | A signed PS Form 3587, a sample piece and any do-not-deliver addresses. | Fill in the carrier route information on the back of the form. |
| Content that is not allowed | No personal information, handwriting, typewritten matter or bills. | Keep the piece generic: a “Postal Customer” offer, not a personalised letter. |
If you use a printer who mails for you
The bundling, facing slips, PS Form 3587 and the drop are done for you, which is most of what the “mailing and prep” line in the cost guide pays for. The one thing left on your side is the artwork: size, postage area and no personal data.