Ready to mail your tax return—or your request for an extension?

Before you pop that envelope into the mailbox, you’ll want to do a little planning. This year, timely mailing isn’t as easy as dropping a properly addressed tax return into the box and walking away. A recent change by the U.S. Postal Service (USPS) has upended what we typically think of as the mailbox rule.

As a first-year law student, I learned it this way: If a piece of mail is properly addressed with the correct amount of postage and dropped in the mailbox, the postmark stamped on the envelope is generally considered the date of filing (or, in contract law, the date that an offer was made). Today, the mailbox rule can also apply to other means of communication, such as fax, telegram, or email.

The concept is particularly important in tax law. It was codified in 1954, when Section 7502 was added to the tax code. By law, a tax return or payment is considered filed on the date of the U.S. postmark, not the date the IRS receives it. For years, this meant that taxpayers could mail returns and checks up to and including the filing deadline, confident that a timely postmark would protect them from penalties and interest. The mailbox rule has long been relied on in tax audits and in Tax Court—until now.

A recent change in USPS processing rules could change all of this. The USPS has clarified that most postmarks reflect the date of postal processing, not necessarily the date that a piece of mail was deposited by the sender. Since most postmarks are applied at processing facilities, they do not necessarily represent either the place or the date where the Postal Service first accepted possession of the mailpiece. This means the date stamped by a postmark applied at a processing facility may be later than the date the mailpiece was first accepted by the Postal Service.

The change, published in the Federal Register on November 24, 2025, became effective on December 24, 2025.

You can see how this could create problems—especially for taxpayers. If your return is dropped into a mailbox on April 15 but not processed until April 16 or later, the machine postmark may reflect the later date.........

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