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Postal Encyclopedia

Flat

Large envelope/catalog-sized mail

Preparation & ProductionUpdated 2026-07-24

A mailpiece larger than letter size, such as a large envelope or catalog, that stays flexible and meets USPS flat-size standards.

Definition reviewed 2026-07-24. This is a plain-English Plavidian reference; for USPS terms, the Domestic Mail Manual is the authority. For your own job, the final mail class, postage, and preparation are confirmed after list processing and production review.

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