Postcards are one of the lightest things you will ever ship, and that should make them the easiest. For most sellers it does. But postcard shipping on eBay has a quirk that trips people up, and it sits right at the intersection of two things that sound like they should get along: protecting a flat piece of cardstock and keeping the envelope flexible enough for the mail stream to process it.
The service at the center of this is the eBay Standard Envelope. Understanding what it is, what it requires, and where it stops being the right choice is most of the job.
What the eBay Standard Envelope actually is
The eBay Standard Envelope is a letter-rate shipping option built into the platform for specific categories of small, flat, lightweight items. Postcards are one of those categories, alongside trading cards, stamps, coins, and a handful of others added over time. It carries integrated tracking that uploads to the order automatically and includes a shipping protection plan on each shipment.
The draw is the rate. Compared to a tracked package service, the cost is a fraction of what a package label would run. For a seller moving individual postcards or small lots, that gap is the difference between a shipping cost that makes sense and one that eats the sale.
But the low rate comes with conditions, and the conditions are mechanical.
The weight and thickness limits
The eBay Standard Envelope tops out at three ounces. A single postcard weighs almost nothing, so that limit is generous for the item itself. Where it tightens is when you start adding protection.
Thickness is the harder wall. The envelope cannot exceed a quarter of an inch at any point, and it must remain uniformly flat, no lumps, no rigid spots that push one area thicker than the rest. That quarter-inch ceiling is a USPS standard for letter-class mail, not an eBay invention, and the Postal Service means it across the whole piece.
A standard postcard, even a thick vintage one, is nowhere near a quarter inch on its own. The trouble starts with what you put around it.
The flexibility rule, and why it matters more than thickness
Here is the part that catches postcard sellers who pack the way they pack everything else.
The Postal Service requires that a letter-class mailpiece and its contents bend easily when subjected to the tension of the automated sorting equipment. The formal standard, published in the Domestic Mail Manual, is that the piece must bend around an eleven-inch-diameter drum under forty pounds of belt tension. In practical terms, that means the envelope has to be flexible. Not floppy, but genuinely able to curve through the rollers of a high-speed sorting machine without jamming.
An envelope that is too rigid to pass through that equipment is classified as nonmachinable. A nonmachinable letter does not simply sail through at a higher rate. It gets pulled, surcharged, delayed, or in some cases returned. The surcharge alone adds meaningfully to a sub-ounce shipment that was supposed to be cheap, and the delay is its own problem when a buyer is watching tracking.
This is the rule that makes postcard shipping different from dropping a greeting card in the mail. A postcard is stiffer than a sheet of paper, stiffer than a birthday card, and depending on the stock, stiff enough to push a thin envelope past the flexibility threshold the moment you add a holder or a sheet of backing board.
Sleeving without failing the test
The instinct from other collectibles categories is to reach for a rigid toploader, the hard plastic sleeve that trading card sellers use for singles in a tracked package. That is exactly the wrong move here. A toploader makes the envelope rigid across its full face. It will not bend around anything, and the sorting machine will reject it or damage it trying. Sellers who have tried report nonmachinable surcharges, returns to sender, and postage-due notices landing on the buyer.
What works is a thin, flexible sleeve. A penny sleeve, the kind used for raw trading cards, is thin enough that it adds almost no rigidity and almost no thickness. The postcard sits inside the sleeve, the sleeve goes inside the envelope, and the whole thing still bends. For a little more structure, a sheet of plain paper folded around the sleeved postcard gives a buffer against scuffing without turning the envelope into a board.
Semi-rigid holders are the middle ground sellers argue about. A semi-rigid holder can work for a single postcard in a properly sized envelope, but it is closer to the line than most sellers realize. Stack two, or pair one with a postcard on heavier stock, and you are likely past the standard. The safe rule: if the loaded envelope resists bending when you flex it in your hands, the sorting machine will have the same opinion, and the machine does not give you a second chance.
How many postcards fit in one envelope
eBay limits the number of postcards you can send in a single Standard Envelope shipment. The cap is lower than you might expect, and lower than the trading card limit. Where trading cards can go up to fifteen raw cards in one envelope, postcards are limited to a smaller count per shipment based on the service’s terms.
The reason is not weight. The reason is the flexibility test again. Postcards are larger and stiffer per piece than a standard trading card, and there is no thin standard sleeve for postcards the way there is for trading cards. Each additional postcard adds rigidity, and by the time you have a handful stacked in an envelope, the package no longer bends the way letter-class mail must. The sorting equipment is the arbiter of that, not your hands.
If you are selling a lot of postcards as a single order, the Standard Envelope is probably not the right service. That is not a flaw. It is a signal to step up.
When to upgrade to a tracked package
The Standard Envelope is built for cheap, light, low-value singles and small lots. It does that job well. But there are clean reasons to leave it behind and send a postcard as a package instead.
Value is the first. The Standard Envelope carries a shipping protection cap, and the current figure sits on eBay’s own Standard Envelope page. If your postcard sells above that cap, you are shipping something worth more than the service was designed to cover. A tracked package with protection that matches the sale price is not an upgrade at that point. It is the baseline.
Quantity is the second. A lot of five or ten postcards is a package, not a letter. The thickness, the rigidity, and the weight all push past what the Standard Envelope can carry. Forcing a multi-card lot into an envelope built for one or two is how sellers end up with surcharges, damaged inventory, or both.
Rigidity is the third. If the postcard is unusually thick, mounted on board, a real photo postcard on heavy stock, or if the only way to protect it properly is a rigid holder, then the item does not belong in a letter. A padded envelope or a small box, sent as a tracked package, lets you protect it properly without fighting the mail stream.
The cost difference between the Standard Envelope and a package is real. But for a postcard worth protecting, the package rate is the cost of doing the job right, and it comes with full tracking from pickup to delivery.
The envelope itself
Use a standard number ten envelope or a similar rectangular envelope that meets the USPS letter-size dimensions: between five and eleven and a half inches long, between three and a half and six and one-eighth inches high, with an aspect ratio between 1.3 and 2.5. A square envelope is nonmachinable by definition. Keep the address label parallel to the long edge and flat against the surface, not folded over a lump.
Do not use a bubble mailer or a padded envelope. Both can push past the quarter-inch limit, and both change the flexibility of the piece. If you need a padded mailer, you need a package service, and that is fine.
What carries over
Ship a single postcard or a small lot in the eBay Standard Envelope when the items are light, low-value, and flexible enough to pass through automated sorting without jamming. Sleeve the postcard in something thin. Skip the rigid toploader. Check that the loaded envelope still bends. When the value, the quantity, or the rigidity of the postcard itself pushes past what the Standard Envelope was built for, step up to a tracked package and price that into the listing. The service is good at what it does, and the cleanest way to use it is to know where it stops.
How to pack a record for shipping is a different method entirely, and it is its own piece in this group. The question of what qualifies for Media Mail, including what does not, is covered separately as well.