PS Form 3665: Certificate of Mailing Explained

PS Form 3665, the Certificate of Mailing, provides official proof that you mailed an item on a specific date without the cost or features of certified mail. This USPS service is ideal when you need to prove you mailed something by a deadline but do not need tracking or delivery confirmation. This guide explains what a Certificate of Mailing is, when to use it, how to fill out PS Form 3665, and how it compares to certified mail.

What is a Certificate of Mailing?

A Certificate of Mailing is a USPS service that provides an official receipt showing you mailed an item on a specific date. The postal clerk stamps PS Form 3665 with the date and gives you a copy as proof. Unlike certified mail, a Certificate of Mailing does not include tracking, delivery confirmation, or proof that the recipient received the item. It only proves you handed the mail to USPS on that date. The mail is delivered as regular First-Class Mail with no special handling or signature required.

When to Use PS Form 3665

Use a Certificate of Mailing when:

• Tax filings: Prove you mailed your tax return by the IRS deadline
• Legal deadlines: Show you submitted documents or notices by a required date (similar use case to return receipt services)
• Business correspondence: Document when you sent contracts, invoices, or official letters
• Insurance claims: Prove you filed a claim or submitted paperwork on time
• Government filings: Meet submission deadlines for permits, applications, or responses
• Cost-sensitive situations: Need proof of mailing but cannot justify certified mail fees

If you need proof the recipient received the item, use certified mail instead.

How to Fill Out PS Form 3665

Step 1: Item Description

Describe the mailpiece. Include enough detail to identify it later (e.g., "Tax return for 2024," "Contract to ABC Company," "Insurance claim #12345"). You do not need to include the recipient address, but you may add it for your records.

Step 2: Number of Pieces

Indicate how many pieces you are mailing with this certificate. If mailing one item, write "1." For bulk mailings, list the total number of pieces.

Step 3: Postage Information

The clerk will calculate postage based on the weight and class of mail. Regular First-Class postage applies, plus the Certificate of Mailing fee.

Step 4: Submit at Post Office

Hand the form and your mailpiece to the postal clerk. The clerk will weigh the item, affix postage, stamp the form with the date, and return a copy to you. Keep this stamped copy as your official proof of mailing.

Certificate of Mailing vs Certified Mail

Understanding the differences helps you choose the right service:

For more details on certified mail, see our PS Form 3800 guide.

Costs and Fees (2025)

• Firm sheet (small quantities): Around $0.60–$0.65 per piece, minimum 3 pieces, plus regular First-Class postage
• Bulk (per-1,000 structure): Around $11–$12 for the first 1,000 pieces and around $1–$2 for each additional 1,000 pieces
• Single-piece alternative: For one-off mailings, check with your local post office for current pricing options

Certificate of Mailing fees are significantly lower than certified mail ($5.30 + postage), making it cost-effective when you need proof of mailing but not delivery confirmation. Rates may vary; verify current fees at usps.com or your local post office.

Bulk Certificate of Mailing

If you are mailing multiple items and need proof of mailing for all of them, use PS Form 3665 in bulk mode:

• List all items on one form (similar to PS Form 3877 for certified mail)
• Describe each piece or attach a list of items
• For large volumes, bulk pricing uses a per-1,000 structure (around $11–$12 for first 1,000, around $1–$2 per additional 1,000 as of 2025)
• For smaller quantities, firm sheet pricing (around $0.60–$0.65 per piece, minimum 3) may apply
• USPS stamps the form and returns a copy covering all items

Is a Certificate of Mailing Legally Valid?

Yes. PS Form 3665 with a USPS date stamp is accepted as official proof of mailing in legal proceedings, tax filings, and business disputes. It proves you handed the mail to USPS on that date. However, it does not prove delivery or that the recipient received the item. Courts, IRS, and government agencies generally accept Certificate of Mailing for deadline compliance, but some situations require certified mail with proof of delivery.

FAQs

Related Guides

• What is Certified Mail?
• How to Fill Out PS Form 3800
• PS Form 3877: Firm Mailing Book
• What is Registered Mail?