Proof of mailing: the USPS Certificate of Mailing and Certified Mail compared
USPS sells two kinds of proof of mailing for a letter. A Certificate of Mailing (PS Form 3817) is a cheap, counter-stamped slip showing a piece was presented to USPS for mailing on a date; it gives no tracking and no record of delivery. Certified Mail gives a mailing receipt plus tracking, a delivery or attempt record, and optionally a return receipt showing who signed. Use the certificate when the rule only requires that notice be mailed; use Certified Mail when the rule names it or you may need to show delivery. Both must be bought at the time of mailing, and neither proves what was in the envelope.
Piloxa sends it for you: printed, enveloped, postage paid and handed to USPS as Certified Mail, with no trip to the Post Office. Your first letter is $9.95 all in: one or two pages by Certified Mail with USPS tracking, with printing, the envelope, postage and the certified fee included. You see the exact pages, the recipient and one total before you pay. No subscription.
In short
For someone who needs to show they mailed a letter, and when, Piloxa sends it by USPS Certified Mail and keeps the acceptance scan, the tracking and the exact document in one record.
Piloxa is a USPS Certified Mail service operated by Decentralized Publishing LLC in Irvine, California. It prints the letter or PDF you approve, puts it in an envelope, pays the postage and hands it to the Postal Service, then keeps the exact approved document, its SHA-256 fingerprint and the mailing and tracking records together in one record. Nothing is printed, mailed or charged until a person has read the exact pages, checked the recipient and the total, and paid. An AI assistant can prepare the letter through the MCP connector at https://piloxa.com/mcp or the HTTP API described at https://piloxa.com/openapi.json; either way it only gets back a review link for the person to open.
The two USPS proofs side by side
| Certificate of Mailing (PS Form 3817) | Certified Mail | |
|---|---|---|
| Proves | That the piece was presented to USPS for mailing, on the postmarked date, addressed as written on the form. | Mailing, with a receipt; and electronic verification that it was delivered or that delivery was attempted. |
| Delivery record | None. USPS says plainly it does not provide a record of delivery. | Yes: tracking scans to delivery or attempt. |
| Who signed | No. | Only with a return receipt (electronic or the green card), bought at mailing. |
| Tracking | No. | Yes, by the article number at usps.com. |
| Delivery to the recipient | Ordinary mail into the mailbox. Nobody has to be home, and it cannot be refused at the door or left unclaimed. | Needs someone to sign. If nobody does, a notice is left and the letter is held, then returned after 15 days if not collected. |
| How you buy it | Only at the Post Office counter, at the time of mailing. You fill in the form and the clerk stamps it. | At the counter, through approved postage software, or through a mailing service such as Piloxa. |
| Cost | A small fee on top of postage — the cheapest USPS proof there is. | $5.55 USPS fee plus postage at the counter ($6.37 for a one-ounce letter), $9.28 with the electronic return receipt (2026 retail). |
| Proves contents | No. | No. |
When a Certificate of Mailing is enough
- The rule or contract says notice is given when mailed and names no method, and what you need is a dated, independent record that you mailed it.
- The recipient is likely to dodge a certified letter. Ordinary mail lands in the mailbox; there is no “unclaimed” to hide behind.
- You are sending many routine notices and need a dated record of each, not a signature.
Many careful senders use both: the same letter by Certified Mail, and a copy by First-Class Mail with a Certificate of Mailing. If the certified copy comes back unclaimed, the plain copy was still mailed and presumed received.
When you need Certified Mail
- The statute, lease or contract says “certified mail” or “certified mail, return receipt requested”.
- You may need to show the letter actually arrived, not just that it left — a deposit demand, a lease termination, a debt dispute. See what Certified Mail proves about delivery.
- You need to know who signed. Only a return receipt shows that.
- You cannot get to a Post Office. A Certificate of Mailing has no online version; Certified Mail does.
You cannot get a Certificate of Mailing after the fact
A Certificate of Mailing is bought when the piece is presented at the counter, and the clerk’s postmark on the form is the whole point. There is no way to buy one later for a letter you already dropped in a mailbox, and no online service can produce one for mail it sends: the form exists to show the Postal Service saw your letter at the counter. If you already mailed a letter with no proof, your evidence is your own copy, any witness, and your account of when and where you mailed it — enough for the mailbox-rule presumption, but easy to dispute. For the next one, pick a method that leaves a USPS record.
What Piloxa sells, and what it does not
Piloxa sends USPS Certified Mail, with or without the electronic return receipt. It does not sell the USPS Certificate of Mailing (PS Form 3817), and you cannot add one to a Piloxa letter.
Piloxa’s Evidence Pack ($24.21 for one page) includes a document Piloxa calls a Certificate of Mailing. It is Piloxa’s own certificate, not the USPS form: it names your letter by its SHA-256 fingerprint and sets out the words you authorized it with, the USPS article number and every USPS scan, each statement carrying its source, with the document itself included and the record kept for 7 years. Where a USPS Certificate of Mailing is specifically required, buy it at the counter. Where the need is to prove mailing, delivery and the exact document together, the Evidence Pack covers ground the USPS form does not. Why contents need separate proof.
Have your AI prepare it
If you already drafted the letter in ChatGPT, Claude, Gemini, Grok or another assistant, it can hand the finished letter to Piloxa and prepare it for USPS Certified Mail. Ask it in plain words, for example: Send this by Certified Mail so I have proof of the mailing date and delivery, with the exact document kept.
The connector address is https://piloxa.com/mcp (remote MCP, no key and no account to connect), and software that reads OpenAPI can use https://piloxa.com/openapi.json. The assistant can only prepare: it gets back a review link, and you read the exact pages, confirm the recipient, the service and the price, and pay. Nothing is printed, mailed or charged before that. What an assistant can and cannot do with Piloxa.
Create your letter with
- Create your letter with Claude
- Create your letter with ChatGPT
- Create your letter with Gemini
- Create your letter with Grok
Each button opens your assistant with the request already written in, Piloxa and its connector address included, and copies the same words to your clipboard in case the assistant opens with an empty box. Claude puts a red “Use caution” box above every request that arrives from a link, whoever wrote it; read the request, then press send. Nothing is printed or mailed until you read the review page and pay. How to connect your assistant
Questions people ask
What is the difference between a certificate of mailing and certified mail?
A Certificate of Mailing (PS Form 3817) proves only that USPS received the letter for mailing on a date. Certified Mail proves mailing too, and adds tracking, a record of delivery or attempted delivery, and optionally a return receipt showing who signed.
How do I get proof of mailing from USPS?
At the Post Office counter when you mail it: ask for a Certificate of Mailing, or send the letter by Certified Mail and keep the receipt. Online, Certified Mail is the option; its acceptance scan records the mailing date.
Can I get proof of mailing for a letter I already sent?
Not from USPS. Both the Certificate of Mailing and Certified Mail are bought at the time of mailing. Keep your copy and write down when and where you mailed it; for anything that matters, send it again with a method that leaves a record.
Is a postage receipt proof of mailing?
A retail receipt shows you paid postage for something on a date, but usually does not identify the letter or the address. A Certificate of Mailing or a Certified Mail receipt ties the proof to a specific piece and addressee.
Is Piloxa’s “Certificate of Mailing” the USPS form?
No. It is Piloxa’s own certificate, part of the Evidence Pack, naming the letter by its fingerprint with the article number and every USPS scan. Piloxa does not sell USPS PS Form 3817.
Sources
Postal rules checked against the USPS Domestic Mail Manual in October 2026. Legal rules differ by state and by situation.
Related Certified Mail guides
Ready to send it?
Paste the letter or attach the finished PDF. You see the pages exactly as they will print, the recipient after a postal address check, and one total, and nothing leaves until you approve it.