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It's the cheapest proof you mailed something that most people never hear about: a post office clerk stamps a form confirming you presented the item on a specific date. It proves when you mailed it, not that it arrived and not what was inside. You can only get it at a post office counter, not online, which is probably why it stays obscure.
The certificate is a simple thing: a USPS form (Form 3817) on which the clerk lists the item you are mailing and stamps it with the date. It is the post office's official statement that on this date, you handed them this item. That is all it says, and the modesty of the claim is the point. It is the least expensive mailing proof USPS sells, precisely because it promises the least.
Here is how it stacks up against the other proof options people confuse it with:
| Service | Proves | Does not prove | Where you get it |
|---|---|---|---|
| Certificate of Mailing | The date you mailed the item | Delivery, or what was inside | Post office counter only |
| Certified Mail | Mailing, tracking, and delivery | What was inside | Counter or online services |
| Return receipt (green card) | Someone signed for it, and when | That the named recipient signed | Added to certified or registered mail |
| Postmark on your envelope | Roughly when it entered the system | Nothing officially; it is just a cancellation mark | Automatic, no request needed |
Notice what the certificate shares with certified mail: neither one says a word about the contents of the envelope. If the contents might be disputed, you need your own records: a dated copy with the mailing details written on it.
Whenever the mailing date is the whole ballgame. The classic case is tax and legal deadlines: the IRS treats a return as filed on time if it was timely mailed, so the certificate is dated proof that you beat the deadline even if the envelope arrives late. The same logic applies to court filings with mailing-based deadlines, contract notices that must be sent by a certain date, and insurance claims where the mailing date starts a clock.
It also shines in bulk. One form can list multiple pieces mailed at the same time, so a landlord sending notices to twenty tenants, or a business sending a batch of invoices, can get dated proof for the entire batch on a single stamped form. That is a fraction of the effort and cost of certifying each piece, when all you need is proof of the mailing date.
At a post office counter, and only there. You cannot buy a Certificate of Mailing online, through a kiosk, or from a third-party mailing service: a clerk has to see the item, list it on the form, and stamp it. Bring the item ready to mail with postage on it, ask the clerk for a Certificate of Mailing, and keep the stamped form somewhere safe. The fee is small and flat per piece, which is why it is the cheapest proof option on the menu.
The counter-only rule is probably why most people have never heard of it. Everything about modern mailing pushes toward online, and this one service stayed stubbornly analog. If you are already going to the post office for stamps or a money order, adding the certificate takes under a minute.
Canada Post does not offer an exact one-to-one equivalent of the USPS Certificate of Mailing as a standalone counter product. The closest options are Canada Post's Registered Mail, which provides proof of mailing and delivery but costs more, and simply keeping the retail receipt from the post office, which shows the date and the service purchased. If you mail through LetterAgent to a Canadian address with the registered option, you get Canada Registered Mail with tracking and proof of delivery, but that is the fuller (and pricier) proof, not the bare mailing-date certificate.
Ready to mail it? Send your letter with LetterAgent: describe it to your AI assistant, approve the exact quoted price, and it is printed and mailed.
LetterAgent is a working name. Prices include print, postage, and our service fee. US prices in USD, Canadian prices in CAD (Canadian prices exclude applicable sales tax, added at checkout). Currently in private testing.
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