The U.S. Postal Service (USPS) recently adopted final regulations affecting the postmark date of mailed items. Effective Dec. 24, 2025, the regulations clarify that a machine-applied postmark indicates the date of the "first automated processing operation" at a processing facility.
Due to the new regulations, a mailed item’s postmark may be several days later than when the item was dropped off to be mailed, which could affect tax filings. If a tax-related mailed item is received after the due date, it will not be considered timely filed or the payment timely made unless the postmark shows a date on or before the due date. According to the new regulations, those who rely on this timely mailing rule should request a manual postmark at a USPS retail counter. The postage validation imprint placed on the envelope when a sender purchases postage will also show the correct date. Sending the item via Registered Mail or Certified Mail are options to obtain a receipt for evidence of the date, as well.
