Certificate of Mailing vs. Affidavit of Mailing: What's the Difference?
A Certificate of Mailing is a USPS-issued receipt proving a mailpiece was accepted into the mail stream on a specific date, while an Affidavit of Mailing is a statement, signed by the sender or the mailing service, declaring what was mailed, to whom, and when. The certificate comes from USPS and proves acceptance; the affidavit comes from the sender and proves intent and content. Neither one proves delivery, which is why many mailers use them alongside Certified Mail rather than instead of it.
What Is a Certificate of Mailing?
A Certificate of Mailing is issued by the United States Postal Service and confirms that a mail item was accepted into the mail stream on a specific date at a specific location. It is official proof of mailing, useful for meeting filing deadlines and regulatory requirements.
It does not include tracking or delivery confirmation. It validates mailing only.
Common Uses
- Tax filings and IRS deadlines
- Court-ordered notices
- Homeowners association notices
- Government communications
- Employment-related documentation
These certificates are widely accepted in legal and government settings when timely mailing must be proven.
What Is an Affidavit of Mailing?
An Affidavit of Mailing is a signed declaration verifying that the sender prepared and mailed a document to the intended recipient. It typically records the recipient's name and address, the mailing date, and a description of the contents.
Unlike the Certificate of Mailing, which USPS issues, an Affidavit is generated by the sender or the mailing service provider. In some jurisdictions an affidavit may be notarized for additional legal credibility; our full-service mailing includes a notarized Affidavit of Mailing with every order.
When Is an Affidavit of Mailing Used?
Affidavits are often used to supplement a Certificate of Mailing, particularly in:
- Court filings
- Lease termination letters
- Compliance and regulatory correspondence
- HR notices
- Landlord-tenant communications
Affidavits help establish that a responsible party mailed the document as described, which can be invaluable in disputes or audits. For a deeper walkthrough, see our guide on affidavits of mailing and same-business-day mailing.
Key Differences at a Glance
| Feature | Certificate of Mailing | Affidavit of Mailing |
|---|---|---|
| Issued by | USPS | Sender or mailing platform |
| What it proves | The item was accepted into the mail stream on a specific date | The sender prepared and sent the described document to the recipient |
| Legal admissibility | Yes, as USPS documentation | Yes, as supplemental evidence; notarization strengthens it |
| Includes proof of mailing | Yes | Yes |
| Includes proof of delivery | No | No |
| Included with Certified Mail Labels | Yes, at no extra cost | Yes, at no extra cost |
| Delivery date shown | No | No |
| Most useful in | Regulatory, tax, court, and audit scenarios | Legal, HR, and procedural documentation |
Why You May Need Both
Using both documents provides layered protection in a legal or regulatory dispute: the certificate shows the item was mailed, and the affidavit adds a declaration of what was mailed and by whom. That combination is especially useful in wage disputes, lease termination timelines, benefit eligibility deadlines, and tax penalty appeals.
One important note on deadlines: the postmark alone is not a guaranteed indicator of the date USPS first accepted a mailpiece, because USPS has clarified in its Domestic Mail Manual that machine-applied postmarks reflect processing dates and may not align with acceptance. For deadline-driven mailings, use services that document acceptance directly, such as Certified Mail or a Certificate of Mailing.
What Neither Document Proves: Delivery
Both documents stop at the mailbox. If your situation requires proof that the item reached the recipient, add Certified Mail for tracking and an acceptance record, plus a Return Receipt for the recipient's signature. The Electronic Return Receipt delivers that signature as a digital record at a lower cost than the paper card, and everything lands in your 10-Year Compliance Archive. You can compare the current cost of each extra service on our USPS rates page.
Get Both Documents Every Time You Mail
At Certified Mail Labels, both a Certificate of Mailing and an Affidavit of Mailing (when selected) are available for every Certified Mail and First-Class Mail letter created on the platform at no additional cost, along with:
- You'll skip the trip to the Post Office entirely; create and print labels online in seconds.
- You'll receive USPS postmarked certificates, timestamped affidavits, real-time tracking, and Electronic Delivery Confirmations automatically.
- You won't pay monthly fees, sign contracts, or lease equipment; pay as you mail.
- You'll get secure 24/7 access to every record in your complimentary 10-Year Compliance Archive.
For organizations with recurring mailing needs like lease renewals, rent increases, or employee notices, Excel batch processing and API and SFTP integrations automate the whole workflow, and our Print & Mail fulfillment prints, inserts, and posts uploaded PDFs the same business day for orders by 5:00 PM Eastern. Whether you're sending one piece or one thousand, schedule a live demo and see the documentation build itself.
Frequently Asked Questions
What is the difference between a Certificate of Mailing and an Affidavit of Mailing?
A Certificate of Mailing is issued by USPS and proves a mailpiece was accepted into the mail stream on a specific date; an Affidavit of Mailing is signed by the sender or their mailing service and declares what document was mailed, to whom, and when. The certificate is third-party proof of acceptance, the affidavit is a sworn statement of the sender's action.
Does a Certificate of Mailing prove delivery?
No. A Certificate of Mailing proves only that an item was accepted for mailing on a specific date; it does not include tracking or delivery confirmation. For proof of delivery you need Certified Mail tracking, ideally with a Return Receipt showing the recipient's signature.
Does an Affidavit of Mailing need to be notarized?
Notarization is not always required but adds legal credibility in some jurisdictions, and some courts and agencies prefer or expect it. Full-service mailing through Certified Mail Labels includes a notarized Affidavit of Mailing with every mailing.
When should I use both a Certificate of Mailing and an Affidavit of Mailing?
Use both when a dispute or audit is plausible: the certificate documents that USPS accepted the mail on a date, and the affidavit documents what was sent and by whom. Together they create layered evidence for wage disputes, lease terminations, benefit deadlines, and tax appeals.
Is a postmark enough to prove when mail was sent?
Not always. USPS guidance clarifies that machine-applied postmarks reflect the date of processing and do not necessarily match the date the Postal Service first accepted the piece, so deadline-critical mailings should rely on Certified Mail or a Certificate of Mailing rather than the postmark alone.
How long should I keep proof of mailing documents?
Keep them as long as the underlying obligation could be questioned, which for many compliance and legal purposes means years. Certified Mail Labels stores certificates, affidavits, tracking, and delivery records in a searchable archive for ten years at no additional charge.