Size qualifies for mail class

First-Class postcard rate needs a piece no larger than 4.25" x 6". EDDM Retail needs a flat-size piece (taller than 6.125" or longer than 11.5").

How to fix it

A 6x9 sent First-Class mails at letter rate, not postcard rate. EDDM Retail requires flats like 6.25x9 or 6.25x11.

Reference

DMM 201.1.1 Postcard dimensions; EDDM Retail (DMM 140)

Catalog version DMM 2026-07. Always confirm against the current Domestic Mail Manual.