Can I mail an oversized postcard without an envelope?

Absolutely. Cards up to 6 by 9 inches can be mailed without an envelope. They simply lose the discounted postcard rate once they pass 4.25 by 6 inches, so larger cards mail at the First-Class letter rate instead.

• No envelope needed: postcards up to 6 x 9 in mail on their own.
• Rate change: anything over 4.25 x 6 in moves to the letter rate.
• Design tip: a scannable QR code lets recipients respond the moment they see the card.