Effective December 24, 2025, the United States Postal Service (“USPS”) finalized new regulations governing postmarks “clarifying” that postmarks are not necessarily indicative of the date an item was mailed or received by the Postal Service. While this clarification may affect how postmarks are treated in areas from mail-in ballots to the “mailbox rule” under contract law, it also bears on an important feature of tax procedure: the “postmark rule” of Section 7502 of the Internal Revenue Code.

The Internal Revenue Code prescribes myriad deadlines for filing items with the IRS, including not only annual income tax returns (famously due on April 15 for individuals) but also numerous other information returns, election notices and other documents that must be timely filed in order to be effective or to avoid penalties. Ordinarily, these documents are deemed filed on the date they are actually delivered to the IRS. Under Section 7502, however, an item mailed by U.S. mail will be treated as delivered on the date the item is postmarked. In years past, many post offices would have extended hours on April 15 and October 15, even staying open until midnight, to allow taxpayers to take advantage of this rule for their annual returns. This practice has largely been abandoned as taxpayers have shifted to filing their annual returns electronically, and IRS statistics show that, even for individual taxpayers, the vast majority of annual tax returns (including schedules and attachments) are filed electronically. Many statements and elections employed by the most sophisticated taxpayers, however, must still be physically mailed, including Form 8832 (to make a “check-the-box” election as to an entity’s tax classification) and notices by corporations confirming that they have provided certifications that they are not U.S. real property holding corporations (often furnished in connection with cross-border M&A transactions).

According to the preamble to the USPS’s new rule, however, the postmark was never intended to be the date on which a piece of mail was first accepted by the Postal Service. While there was always a possibility of a misalignment between postmark date and acceptance date, the USPS expects that this likelihood may increase as the USPS advances new logistics initiatives that seek to centralize mail processing through regional processing and distribution centers that may be remote from local post offices. Accordingly, the Postal Service explained that it adopted this rule not in order to change its existing practices, but rather to clarify the meaning of a postmark: that it “confirms that the Postal Service accepted custody of a mailpiece, and that the mailpiece was in the possession of the Postal Service on the identified date,” but “does not necessarily indicate the first day that the Postal Service had possession of the mailpiece.”

The implication for taxpayers, therefore, is that simply mailing a return or statement on the filing deadline, even at a post office, is insufficient to ensure that the item will be treated as timely filed. A best practice for taxpayers wishing to take advantage of the postmark rule would be to mail via certified mail with a return receipt. Alternatively, taxpayers can use private delivery services (“PDSs”), which are IRS-approved services offered by FedEx, UPS and DHL, for which the IRS will treat proof of acceptance by the PDS as the equivalent of a postmark.