Can I mail a 5x7 postcard at the postcard rate?

No. A 5 by 7 inch card is larger than the USPS postcard maximum of 4.25 by 6 inches, so it mails at the First-Class letter rate instead of the postcard rate. The size is still popular for direct mail because the extra surface makes the card stand out, but you should budget for the higher postage.

• Why it happens: both the 5 inch height and 7 inch length exceed the postcard-rate limits.
• What it costs: letter-rate postage per piece rather than the discounted postcard stamp.
• When it is worth it: bigger cards tend to grab more attention, which can lift response enough to offset the postage.