Acrylic invitations, wrapped in velvet, tied with twine, sealed with a metal charm. Beautiful — and not letters.
A postal clerk put it plainly: this is a parcel. The difference between $0.78 and $5.40, across 200 guests, is a $924 mistake made silently at the design stage.
Three tests, not one
Mailability is judged on weight, shape and flexibility. Most couples check the first and are caught by the third.
Weight — the easy one
A Forever stamp covers one ounce. A heavy cardstock invitation with a reply card and two envelopes typically weighs 1.2 to 1.6 oz, which means the two-ounce rate at about $1.04.
Shape — the square surcharge
Sorting machines orient by the long edge. A square envelope has none, so it needs the non-machinable surcharge of $0.46.
Rigidity — the one that hurts
A letter has to bend around an 11-inch diameter drum. Acrylic does not bend. Wood does not bend. Anything that fails this is reclassified as a package, and postage goes from around $1.20 to $5.00 and up.
No stamp combination fixes this. It is a class change, not a rate adjustment.
Best deals on Forever stamps
What the butterfly stamp does and does not cover
The butterfly stamp — around $1.23 — covers the surcharge for irregular letters: squares, lumpy envelopes, rigid clasps. It is the right answer for a wax seal.
It is the wrong answer for a rigid invitation. That piece is not an irregular letter; it is a parcel, and it needs a parcel service.
Tiering a mixed mailing
| Tier | Postage required | How to buy it |
|---|---|---|
| Standard paper suites (180) | Two-ounce, ~$1.04 | Surplus Flag at $0.62 plus a vintage 42¢ |
| Lumpy or square | Non-machinable, ~$1.23 | Butterfly stamp, official |
| Rigid keepsake pieces | Ground Advantage, ~$5.50 | A commercial label — no stamps |
The surplus-plus-vintage combination is worth noting: $0.62 paid for a $0.78 face stamp, plus a 42¢ vintage, lands exactly on the two-ounce rate while costing less than buying it new.
The slot test
Cut a 1/4 inch slit in a cardboard box and drop one fully assembled suite through it.
- Slides through cleanly — letter rates apply, roughly $0.78 to $1.20.
- Sticks — you are in flat or parcel territory, and you need to know that now rather than after 200 are stamped.
Sacrificing one sample to find out is the cheapest test available. Technical standards are in Notice 123, with mailpiece design detail on PostalPro.
Ask for hand-cancelling
Anything with a wax seal should be hand-cancelled — postmarked by a clerk rather than run through the machine that would crack it. Go at a quiet hour, bring one sample to show, and ask before handing over the stack.
Where to buy
The USPS official store for two-ounce and non-machinable stamps, or a verified surplus channel such as Forever Stamp Center for the base-layer stamps in an array.
The short version
Weigh it, measure the aspect ratio, and bend it. If it will not bend, it is a parcel and no stamp will save you — decide that before the order is printed, not at the counter.
More on buying Forever stamps
- 👉 Forever Stamp Buying Checklist: What to Know Before You Order
- 👉 The Miami Open-Rate Secret: Why I Use Psychology (and Stamps) to Sell
- 👉 The Vegas Spread: How I Built a Cash Flow Fortress Using Stamps
Currently working at USPS in Chicago, he has more than 15 years of experience in bulk mailing and logistics. His columns focus on Forever Stamp trends, helping businesses and individuals make cost‑effective mailing decisions.
