Overview
Effective December 24, 2025, USPS adopted a final rule adding Section 608.11 to the Domestic Mail Manual regarding USPS postmarks. Machine-applied postmarks will generally reflect the date mail is first processed at a regional USPS processing facility, rather than the date an item is deposited at a local post office or mailbox.
As a result of changes in USPS procedures impacting postmark dates, the postmark date on mailed items may be applied days after the item is delivered to USPS. This may cause a return, payment, or other submission that was mailed on or before a statutory deadline to nevertheless receive a postmark dated after the due date.
Because federal and state tax filing deadlines are determined by the postmark date (not the date of deposit), these changes introduce new timing risks for filings and payments submitted by mail across all jurisdictions.
Under current USPS processing procedures, routine mailbox drop-off, including at after-hours post office slots, may no longer reliably produce a same-day postmark.
What This Means for You
The USPS changes alter a long-standing assumption relied upon by taxpayers — that depositing mail with USPS by the filing deadline will result in a timely postmark. Under the revised processing procedures, this assumption may no longer hold true.