LetterAgent
Mail physical letters by just asking your AI assistant.
Home > Guides > Proof of mailing
The USPS certificate of mailing (Form 3817), stamped by a clerk when you hand over the letter, proves you mailed something on a specific date: not that it arrived, just that you sent it. If you need proof of delivery too, that's certified or registered mail. LetterAgent gives you a proof-of-mailing receipt for every letter once it enters production.
| Proof type | What it proves | What it doesn't prove |
|---|---|---|
| Certificate of mailing (Form 3817) | You handed the item to USPS on a specific date | That it arrived, or what was inside the envelope |
| Certified mail receipt | Mailing date plus tracking and a delivery record | The contents of the letter |
| Registered mail | Chain of custody with signature on delivery | Again, not the contents: keep a copy yourself |
| LetterAgent proof-of-mailing receipt | Your letter entered production on a recorded date and time | Delivery, unless you chose the registered option |
It's the cheapest proof USPS sells, and most people have never heard of it. You bring the letter to the counter, the clerk stamps Form 3817 with the date, and you keep the stamped form. That's it: no tracking number, no delivery confirmation. It exists for one situation, proving you mailed something on time when a deadline is judged by the mailing date, like a tax filing or a notice with a statutory clock. It only covers uninsured domestic mail, and you have to ask for it at the counter; it doesn't happen automatically. Keep the form with your copy of the letter.
Canada Post doesn't sell a standalone certificate of mailing the way USPS does. Your proof options are the receipt from registered mail, which shows acceptance and the delivery outcome, or the proof-of-mailing receipt from a mailing service like LetterAgent, which records when the letter entered production. For anything with a deadline going to a Canadian recipient, registered mail is the standard move: it gives you the stamped receipt, tracking, and signature in one package.
Because they answer different questions. Mailing proof answers "did you send it on time," which is what deadlines care about. Delivery proof answers "did they get it," which is what disputes care about. A surprising number of arguments conflate the two: someone waves a mailing receipt as if it proves receipt, or demands delivery confirmation for a deadline that only required timely mailing. Figure out which question your situation actually asks, then buy the proof that answers it. When in doubt, certified or registered covers both.
Ready to mail it? Send your letter with LetterAgent: describe it to your AI assistant, approve the exact quoted price, and it's 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.
Need help? Ask your assistant: it can check a job's status any time. If it ever can't handle something: hello@getletteragent.com