People search for “proof of mailing” when a date matters more than an arrival. A filing has to be postmarked by the 15th. A lease requires written notice thirty days out. A contract says notice is effective when sent. In all of those, what you need to be able to show later is that the envelope left your hands and entered the mail on a particular day, and the Certificate of Mailing is the small, cheap USPS service built for exactly that and for nothing else.
The trouble is that people buy it expecting more. The most common mistake in this whole corner of the postal system is assuming a Certificate of Mailing will help when a package goes missing. It will not. Everything below is checked against USPS's own documentation, which is linked throughout.
What a Certificate of Mailing actually is
It is an extra service you buy at the moment of mailing. A postal employee takes your form, confirms the item is being presented, applies a round date stamp, and hands the form back to you. That stamped form is the certificate. The USPS International Mail Manual puts it in one sentence: certificate of mailing service provides evidence that mail has been presented to the Postal Service for mailing.
Two details do most of the work in practice. First, the form carries the names and addresses of the sender and the addressee, so it identifies which item was mailed, not just that something was. Second, USPS does not keep a copy. Both the Domestic Mail Manual and USPS PostalPro say the Postal Service does not retain copies of either form. There is no lookup and no phone number that can recover it. DMM 503 does provide for a duplicate of a Form 3817 after mailing, but only if you present the original postmarked certificate, so it is a way to get a second copy and not a way to replace a lost one. Scan the receipt the day you get it.
What it does not do
- It is not proof of delivery. USPS says directly that certificate of mailing service does not provide a record of delivery.
- It is not insurance. USPS states that the fee paid for certificates of mailing does not insure the item against loss or damage. See our note on shipping insurance for how coverage actually works, and the glossary for the short definition.
- It is not tracking. The service adds no article number and produces no scans. If the mailpiece has tracking, that came from the mail class or another extra service, not from the certificate.
- It is not retroactive. It is sold at the time of mailing. You cannot buy one for something you mailed last Tuesday.
- It does not fit every mail class. USPS sets out which extra services can be combined with which classes in Exhibit 1.4.1 of DMM 503. Check there before you build a process around it.
The two forms: PS Form 3817 and PS Form 3665
There is an individual version and a bulk version, and which one you use is purely a question of how many pieces you are presenting at once.
| Form | When it is used | How it works |
|---|---|---|
| PS Form 3817 Certificate of Mailing | An individual piece, presented at a retail Post Office counter. USPS PostalPro describes it as available for fewer than three individual pieces presented at one time. | You fill in sender and addressee, pay the fee, and the clerk round dates it. You keep the form. |
| PS Form 3665 the firm sheet | Three or more pieces presented together, which is the usual case for a law office, a billing run, or a compliance mailing. | Every article is listed on one sheet. USPS charges its certificate fee per article listed, and business mailers can submit the firm sheet electronically and pay from an Electronic Payment System account. |
There is a wrinkle worth knowing before you walk up to a counter with a stack of envelopes. PS Form 3877, the Firm Mailing Book for Accountable Mail, is the firm sheet used for accountable services such as Certified Mail, Registered Mail, insured mail, and Priority Mail Express. The Domestic Mail Manual and PostalPro both name Form 3665 as the certificate of mailing firm sheet, but the USPS retail extra services page tells customers to use PS Form 3817 or PS Form 3877 and does not mention 3665 at all. The two sources are written for different audiences, retail counter and business mail entry, so ask the clerk which form they want rather than arriving set on one.
A third number turns up in high-volume work: DMM 503 covers bulk quantities of certificates of mailing separately, on Form 3606-D, which is a different thing again from evidencing individual pieces.
Certificate of Mailing vs Certified, Registered, Return Receipt and tracking
This is the table worth bookmarking. Read down the “proves delivery” row first, because that single row is where most of the confusion lives.
| Certificate of Mailing | Certified Mail | Registered Mail | Return Receipt | USPS Tracking | |
|---|---|---|---|---|---|
| What it proves | The item was presented to USPS on a given date | You mailed it, and USPS recorded delivery or an attempted delivery | A signed chain of custody from acceptance through delivery, for a declared value | Who accepted the item and on what date | Where and when the item was scanned |
| Proves delivery? | No | Yes. USPS keeps a delivery record that includes the recipient signature | Yes, and delivery requires a signature | Yes. This is the only thing it does | Shows a delivery scan, but no signature |
| Tracking? | No | Yes, via the article number | Yes, recorded at each handoff in the USPS receipt system | No. It is an add-on to a service that has it | Yes. That is the service |
| Insurance? | No. The fee does not insure the item | No coverage from the service itself; any insurance comes from the mail class it rides on | Yes, matching the declared value up to the USPS maximum, which USPS currently lists as $50,000 | No | No, though classes such as Ground Advantage include a base amount of coverage |
| Typical use | Deadline-driven mail where the postmark date is the whole issue | Legal notices, tax filings, anything you may have to prove arrived | Valuables and irreplaceable documents | Added to Certified or Registered Mail when you need the signature back | Ordinary parcels where you just want visibility |
Two caveats on that table. Return Receipt is not a standalone product: it is bought at the time of mailing and attached to an underlying service, in hardcopy on PS Form 3811 or delivered electronically. Registered Mail is the high security option: USPS calls it the most secure service it offers and moves it under a system of receipts that records the item from the point of acceptance through to delivery, which is why it is handled and priced quite unlike anything else in the table. Coverage limits and service details are set by USPS and do change, so confirm them on the USPS extra services page before you rely on any of it.
When a Certificate of Mailing is the right choice
Use it when the date of mailing is the fact in dispute and delivery is not. That is a narrower set of situations than most people assume, but it is a real one:
- Deadlines measured by postmark. Filings, submissions, and renewals where the rule says mailed by rather than received by.
- Contract notices with a “when sent” clause. Plenty of agreements make notice effective on dispatch. Read the notice clause: if it says effective on receipt, this is the wrong service.
- High-volume compliance mailings. A firm sheet lets an office evidence hundreds of notices in one dated document rather than hundreds of separate receipts.
- A hedge against “you never sent it.” When the realistic risk is someone denying that anything was mailed at all, rather than a lost item you need paid for.
When it is not enough
If your downside is that the item never arrives, a Certificate of Mailing does nothing for you. It will not get the item found, it will not pay for it, and it will not persuade anyone that it was delivered.
The clearest illustration is tax filing. Under the Treasury regulation on timely mailing, 26 CFR 301.7502-1, proof that a document was properly registered, or that a postmarked certified mail sender's receipt was properly issued, is prima facie evidence that the document was delivered. The regulation goes on to describe registered mail, certified mail, approved private delivery services, and direct proof of actual delivery as the exclusive means of establishing that presumption. A Certificate of Mailing is not among them. For anything with a statutory filing deadline, spend the extra and send it Certified.
The same logic applies to an eviction notice, a demand letter, or an insurance claim: if the other side can gain by saying it never arrived, buy proof of delivery, not proof of mailing.
What it costs
USPS sets the fee, charges it per article, and revises its prices, usually more than once a year. We do not publish postal fees here because they go stale and a wrong number is worse than none. Check the current fee on the USPS insurance and extra services page or the USPS certificate of mailing FAQ. What is stable is the ranking: a Certificate of Mailing is the cheapest of these services, Certified Mail costs more, adding a Return Receipt costs more again, and Registered Mail is by a wide margin the most expensive.
Does any of this apply to ecommerce orders?
Rarely. Ecommerce parcels ship on classes that already carry USPS Tracking, which is what a customer and a support team actually want: scan events, a delivery scan, and a paper trail if a claim is needed. Our guide to USPS tracking status meanings covers reading those scans, and a delivery exception is usually the event that matters. A Certificate of Mailing has no place in that workflow, because nobody is disputing the date you shipped.
Where it does come up in a warehouse is in the paperwork around the goods rather than the goods themselves: recall notices, regulatory correspondence, and contractual notices to a retailer. Those are letters with deadlines, and that is the kind of mail this service was designed around. We run one warehouse in Austin, Texas, and we handle the outbound fulfillment side; the legal mail stays with you and your counsel.