The New Mailbox Rule
The IRS tends to be very strict about filing deadlines. Just a single day beyond a deadline has been enough to trigger penalties for tardy taxpayers. The general rule has been that if a return has been postmarked by the deadline, it is timely filed. Taking the tax return to the Post Office or depositing it in a mailbox before the posted final pickup has been assumed to be sufficient to satisfy that documentation.
Perhaps not anymore. In November, the Postal Service finalized a proposed clarification of how and when postmarks are applied. Mail may not necessarily be postmarked on the date it is received, and a postmark only means the mail was in the possession of the Postal Service on that date, not that it was deposited on that date. Some mail is sent to regional centers for automated cancellation. The delay may not be significant, but taxpayers should no longer assume that they will get a postmark on the day they drop off a return.
The best approach is to use registered or certified mail for proof of timely mailing. If one takes this approach, it’s important to keep the receipt because the Post Office does not create an archive of this data. Alternatively, one can request a manual postmark at a Post Office. The Postal Service’s advice on tax filings is here: https://www.usps.com/taxes/?utm.
By the way, the postmark from an office postage machine is not determinative for tax filing purposes, it only creates a rebuttable presumption of timely filing. The IRS has been known to successfully rebut that presumption when a return is received suspiciously late.
(January 2026)
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