Postcard Mailing Checklist Before You Drop It in the Mail

A postcard mailing checklist is the short list of size, design, list, and postage checks that keeps your card from getting downgraded to a higher rate — or bounced back to you unopened. Run through it before you approve the print file, not after the box of 5,000 shows up. The rules that trip people up almost always live in the first two steps: the card's dimensions and the empty space you're required to leave for the barcode.

Here's the order that actually saves money. Size first, because it decides which postage rate you're even allowed to pay. Then layout, copy, list, proofing, and drop-off. Skip around and you'll design a beautiful 5×7 card only to learn it doesn't qualify for the postcard rate.

USPS Postcard Size Rules

To qualify for the USPS First-Class postcard rate, a card must be rectangular and fall between 3.5" to 4.25" high, 5" to 6" long, and 0.007" to 0.016" thick. Go outside that box on any single measurement and it's billed as a letter, not a postcard. Larger direct-mail cards ride under Marketing Mail and can run up to 6-1/8" × 11-1/2" × 1/4" thick.

That's why a 5×7 is such a common surprise. It's longer than 6", so it loses postcard pricing and gets charged the letter rate — a small per-piece jump that stings across a 2,000-piece run. An 8.5×11 sheet? Mailable, but it's a flat or a folded self-mailer with its own tabbing and postage rules, never a postcard rate.

Card size	Rate class	Postcard rate eligible?
4×6	First-Class postcard	Yes
5×7	First-Class letter	No — priced as a letter
6×9, 6×11	USPS Marketing Mail	No — postcard rate is letter-size only
8.5×11	Flat / folded self-mailer	No

One more measurement people forget: thickness. Card stock thinner than 0.007" is too flimsy for automated equipment and gets rejected. If you're printing at home or picking a light stock to save money, check the caliper before you commit.

Design and Barcode Clear Zone

Give the machines room to work. On the address side (the right half of the card back), you need to reserve the delivery address block, the indicia or stamp corner, and a clean, print-free strip along the bottom right — roughly 4.25" wide by 5/8" to 1.5" tall — where USPS sprays the Intelligent Mail barcode. Print a background color or graphic into that strip and the scanner can misread it, which slows delivery or kicks the piece to manual handling.

The safest move is to pull a template from your print vendor and design inside its guides. Bleed, trim, and safe-margin lines are already marked, so artwork that runs to the edge won't get sliced and text won't crowd the cut.

• Keep the address block and barcode zone on the right third of the back.
• Leave the barcode strip white or a very light tint — no dark ink, no photos.
• Set a return address (top left of the address side). Undeliverable cards without one are simply thrown away; with one, they come back so you can clean your list.
• Build in a 1/8" bleed and keep critical text 3/16" inside the trim.

Contrast matters more than most designers admit. If your headline is light gray on white, older recipients won't read it, and neither will a phone camera pointed at a QR code. Dark text on a light field, 10-point minimum for body copy.

Copy, CTA, and Contact Info

You have about three seconds before this card goes in the trash pile or the keep pile. Lead with a benefit, not your logo. "20% off your first cleaning" beats "Welcome to our company."

State the offer plainly, give one clear action, and make the response frictionless — a short URL, a phone number, or a QR code that lands on the exact offer page. One call to action, not four. When you split attention across a website, a phone number, a coupon code, and a social handle, response rates drop because the reader has to decide what to do instead of just doing it.

Social proof earns its space if it's specific. "Rated 4.8 by 300 local customers" reads as real. "Trusted by many" reads as filler. And whatever you promise on the card, honor it — a coupon code that doesn't work at checkout burns the trust the mailer was supposed to build.

A note on postage itself: if you're buying stamps rather than using a permit indicia, you'll want denominations that match the postcard rate exactly so you're not overpaying by rounding up to a full letter stamp. Our postcard stamps are Forever-priced, so they stay valid through rate changes — handy for evergreen mailers you'll reprint next quarter.

Mailing List Prep and Format

Your list is where campaigns quietly fail. A well-designed card sent to stale addresses is money set on fire. Format the file as a CSV with each field in its own column: Address, City, State, and ZIP at minimum, plus Name, Company, and Address Line 2 where they apply. One recipient per row, no merged cells, no addresses jammed into a single field.

Run the list through CASS-certified address validation before you print. It standardizes formatting, fills missing ZIP+4 codes, and flags undeliverable rows — which also qualifies you for the automation discounts that make bulk postcards worth mailing.

Then choose your route:

• Your own list — customers and past leads. Highest response, but it needs deduping and a recent NCOA move-update pass.
• A targeted purchased list — filter by ZIP, income, or homeowner status when you're prospecting cold.
• EDDM (Every Door Direct Mail) — no names needed. You pick postal carrier routes and mail to every address on them.

EDDM and a targeted list are not the same workflow, and mixing them up costs you. EDDM has its own minimum card size (larger than a standard 4×6), a per-piece rate paid at the Post Office, a 5,000-piece daily cap per ZIP, and paperwork (PS Form 3587) you fill out at drop-off. A targeted mailing skips the route paperwork but requires a clean addressed list and, usually, a permit. Pick the lane before you design, because the size rules differ.

Pre-Print Proof and Drop-Off

Before you approve anything, run the file through a proofing gate. This is the step competitors bury, and it's the one that prevents an expensive reprint.

1. Open the file at 100% — is every image 300 DPI, not a stretched web JPG?
2. Confirm the color mode is CMYK, not RGB, so print colors match your screen.
3. Check that nothing important sits inside the barcode clear zone or outside the safe margin.
4. Verify the address block, return address, and postage area are all present and unobstructed.
5. Proofread the offer, the phone number, and the URL — then test the QR code with an actual phone.
6. Print one physical card and mail it to yourself. Seeing it arrive tells you more than any on-screen proof.

Then plan the calendar. A realistic timeline runs about 2–4 business days for print production, a day for mail prep and paperwork, and 2–9 days in the mail depending on class — First-Class postcards move in roughly 2–5 days, Marketing Mail in 3–10. Working backward from an event date? Add a buffer; USPS processing slows around the December holidays and tax season.

If you're hand-stamping and dropping a smaller batch yourself, postcard stamps supplier options that ship fast keep this last step from becoming the bottleneck. For anything you need delivered on a firm date, priority mail stamps cover the pieces that can't wait in the standard queue.

FAQ

What are the mailing requirements for postcards?

A postcard must be rectangular, between 3.5"–4.25" high and 5"–6" long, and 0.007"–0.016" thick for the First-Class postcard rate. It also needs a clear address area and barcode zone on the right side of the back.

What are the mailing instructions for a postcard?

Put the delivery address, postage, and return address on the right-hand side, leave the barcode strip blank, apply a postcard-rate stamp, and drop it in any USPS collection box or hand it to your carrier.

Does a 5x7 postcard require extra postage?

Yes. At 7 inches long it exceeds the 6-inch postcard maximum, so USPS charges the First-Class letter rate instead of the lower postcard rate, even though it looks like a postcard.

Can you mail an 8.5x11 postcard?

Not at the postcard rate. An 8.5×11 piece is too large, so it mails as a flat or a folded self-mailer with tabbing requirements and higher postage than a standard postcard.

Run this checklist once and it becomes muscle memory by your second campaign. When you're ready to stamp and send, Mailboxes of Flushing supplies inspected, authentic Postcard Forever Stamps that hold their value through rate changes — so the postage line of your checklist is the easiest box to tick. Browse the collection, match the denomination to your card, and get your mailer out the door.