The Tax Times: USPS Postmark Rule Change: Why “Mailed on Time” May No Longer Mean “Filed on Time”

The U.S. Postal Service adopted a final rule effective December 24, 2025, that changes how postmark dates are determined and it could mean trouble for taxpayers who mail their returns close to the deadline. Under the new framework, a postmark now reflects the date mail is first processed by an automated sorting machine at a regional facility, which may be one or more days later than the date the taxpayer actually dropped it off.

Why This Matters for Tax Filers

Under IRC § 7502's "timely mailing rule," the postmark stamped on a mailed return is treated as the date of delivery to the IRS. This rule has long protected taxpayers who mail returns by the due date but whose returns arrive at the IRS after the deadline. If the postmark falls within the prescribed filing period, the return is deemed timely filed.

The problem is that the USPS's Regional Transportation Optimization (RTO) initiative has increased the likelihood that mail will not arrive at processing facilities on the same day it was collected or dropped off. As a result, a taxpayer who deposits a return in the mail on April 15 could receive a postmark dated April 16 or later, making the return appear late even though it was mailed on time.

The Real-World Consequences

The stakes are significant. A late postmark can trigger denied extension requests, loss of refund claims, or even jurisdictional dismissal of a Tax Court petition. Where the USPS changes produce later postmarks for documents that were mailed on time, a taxpayer may appear to have filed past a statutory deadline with potentially serious consequences.

Best Practices for Paper Filers

The IRS continues to encourage electronic filing as the safest option. For taxpayers who must paper-file, practitioners recommend the following strategies to protect against postmark risk:

· Use certified or registered mail. Under § 7502(c) and Reg § 301.7502-1, the postmark on a certified mail sender's receipt is treated as the postmark date. This also provides prima facie evidence of delivery to the IRS.

· Use an IRS-designated private delivery service. The IRS has designated specific services from DHL Express, FedEx, and UPS that qualify under the timely mailing rule. Only enumerated service types qualify, not every service offered by these carriers.

· Mail earlier. Don't wait until the last day. Build in a buffer of several days before any filing deadline.

· Request a manual postmark. Visit a USPS retail counter and ask for a hand-stamped postmark at the time of mailing to lock in the correct date.

· Obtain a certificate of mailing. This provides an additional contemporaneous record of the mailing date.

The Bottom Line for Practitioners

Even before this USPS change, relying solely on a first-class mail postmark was risky. If the envelope is lost between the post office and the IRS, the postmark alone cannot prove delivery. Certified mail with return receipt requested or a designated private delivery service remains the best practice for any time-sensitive IRS submission. With the April 15, 2026 federal filing deadline approaching, now is the time to advise clients who paper-file to adjust their mailing practices accordingly.

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