USPS Postmark Rule Could Impact Timely Filing of Mailed Documents

Under a new U.S. Postal Service (USPS) rule effective December 24, 2025, the USPS has clarified that a machine-applied postmark indicates the date the item is first processed by USPS using an automated sorting machine, which may be later than the day it was received by the post office. That means a document received by the post office on time could end up with a postmark dated after the deadline.

This can affect a wide range of mailed items, including tax returns and payments, payroll filings, elections, appeals, responses to notices, and other documents where timeliness depends on the postmark date. For tax filings, the timely mailing rule of IRC Section 7502, still applies, but relying on a machine postmark alone may be riskier.

If mailing a document close to a deadline, the USPS recommends one of the following:

Ask for a manual postmark at the retail counter
Use Certified Mail or Registered Mail to get proof of the mailing date
Build in extra time whenever possible