USPS mailing guides, in plain language
The standards that decide what your piece costs and whether it mails at all: sizes, tabbing, addressing, automation, EDDM, and drop shipment. Written from the USPS Domestic Mail Manual by a USPS Full-Service Certified mail service provider, with no jargon and nothing to download.
Every guide
Sizes and design
- Postcard, Letter, Flat, or Parcel: USPS Size LimitsThe USPS size limits that decide whether a piece prices as a postcard, letter, flat, or parcel. As of July 12, 2026, presorted postcards can be up to 6 x 9.
- Folded Self-Mailers and Tabbing RequirementsFolded self-mailer tabbing rules: two 1-inch tabs up to 1 ounce, 1.5-inch tabs up to 3 ounces, where they go, which way to fold, and when no tabs are needed.
- Mailing Booklets: Size, Spine, and Tabbing RulesHow a saddle-stitched or perfect-bound booklet mails at letter prices: the 3-ounce and 0.25-inch limits, spine placement, tab count, and paper minimums.
- Designing Artwork That Mails CorrectlyWhere the address, barcode, and indicia go on letters and flats, the aspect ratio that keeps a letter machinable, and where tabs and folds can and cannot go.
Addressing and lists
- Addressing, CASS, and Move Update RequirementsWhat CASS processing and ZIP+4 coding do for your postage, the Move Update rule (within 95 days before mailing), and how endorsements handle undeliverable mail.
- How to Prepare a Mailing List for Bulk MailSend your list as a CSV or Excel file with separate columns for name, address, city, state, and ZIP. How CASS, Move Update, and deduping affect your postage.
- Intelligent Mail Barcode and Informed DeliveryWhat the Intelligent Mail barcode encodes, where it goes, what Full-Service requires, and how an Informed Delivery campaign adds a color image and link.
Postage, entry and payment
- USPS Mail Classes Explained: First-Class vs Marketing MailBills and statements must go First-Class; bulk advertising usually mails cheapest as Marketing Mail. What each USPS mail class can carry, and how to choose.
- Automation and Presort: How to Earn the Lowest PostageWhat machinable, nonmachinable, and automation mean, the presort minimums, and what a mailing needs to earn the lowest per-piece prices.
- Carrier Route Density: Basic, High Density, and SaturationHow pieces per carrier route set your postage: Basic (10), High Density (125), High Density Plus (300), and Saturation, and when filling a short route pays off.
- Drop Shipment and Destination Entry DiscountsWhat SCF and DDU drop shipment mean, how destination entry lowers postage, the end of the NDC discount in July 2025, and when the freight is worth it.
- USPS Delivery Times by Mail ClassUSPS delivery times by class: First-Class Mail takes 1 to 5 business days and Marketing Mail roughly 3 to 10. How to plan a drop date around them.
- Postage Payment, Permits, and Indicia for Bulk MailHow bulk mail postage is paid (permit imprints, meters, precanceled stamps), why you do not need your own permit to mail with Plavidian, and postage statements.
Special mail
- EDDM: Every Door Direct Mail RequirementsEDDM size and weight rules at the Post Office counter and on a permit, the Retail cap of 5,000 pieces per ZIP Code per day, bundling, and Retail versus BMEU.
- Nonprofit Mail: Who Qualifies and How to Get AuthorizedNonprofit postage rates are only for organizations USPS has authorized. How to apply with PS Form 3624 and which content is restricted at nonprofit prices.
- Political Mail and Official Election MailHow Political Mail differs from Official Election Mail: who sends each, red Tag 57, green Tag 191, the eagle logo, and timing mail around an election.
- Reply Mail: Courtesy, Business, and Qualified Business ReplyCourtesy Reply Mail, Business Reply Mail, and QBRM compared: who pays the return postage, what permits and fees each needs, and how to choose a reply device.
- USPS Extra Services: Certified, Registered, and TrackingWhat Certified Mail, Return Receipt, Registered Mail, Certificate of Mailing, Signature Confirmation, and insurance each do, and which mail classes take them.
- Shipping Parcels: Ground Advantage, Priority, and ExpressWhen a piece ships instead of mails, and how Ground Advantage, Priority Mail, and Priority Mail Express compare on speed, size, and dimensional weight.
Still not sure?
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