New USPS Rule: Be Careful When the Postmark Matters

Important Update Effective December 24, 2025

Many people assume that the date stamped on a piece of mail—the postmark—is the same date the U.S. Postal Service actually received the item. As of late 2025, the USPS has clarified that this is not always the case, and the distinction can matter when legal or tax deadlines are involved.

The New USPS Rule

On November 24, 2025, the U.S. Postal Service adopted a new final rule (39 C.F.R. Part 111), effective December 24, 2025, intended to improve public understanding of how postmarks work.

Under this rule, the USPS clarified that a postmark date does not necessarily reflect the date the USPS first accepted possession of a piece of mail. In many cases, postmarks are applied later at a mail processing facility, rather than at the time and place where the mail was originally dropped off or accepted. As a result, the postmark may be applied one or more days after the USPS actually took custody of the item.

Importantly, the USPS explains that a postmark only confirms that the mail was in USPS custody on the date of the postmark, not necessarily when it was first mailed.

Why This Matters for Legal and Estate Planning Deadlines

This clarification is especially important for documents where deadlines are determined by the postmark date, not the delivery date. Common examples include tax filings, court documents, contractual notices, and certain trust or probate-related mailings.

If a deadline depends on a postmark, relying on routine mailing procedures could create risk if the postmark is applied later than expected. In some cases, a document may be timely deposited with the USPS but still receive a postmark that falls after the applicable deadline.

Practical Takeaways

To avoid disputes or missed deadlines when timing matters, individuals should consider using one of the following options:

• Requesting a manual postmark at the post office counter

• Purchasing a Certificate of Mailing

• Using Certified Mail or Registered Mail, which provides verifiable mailing records

• Using a private delivery service that provides reliable proof of mailing and acceptance dates

These steps can be especially important when sending time-sensitive legal notices, tax documents, or estate planning–related correspondence.

Bottom Line

The USPS postmark should no longer be assumed to reflect the exact date a document was mailed. When deadlines matter, additional proof of mailing can help protect your legal rights and avoid unnecessary delays or disputes.

If you have questions about mailing requirements for legal notices, trust administration, or estate planning documents, it’s always best to ask before sending something time-sensitive.