The USPS changed its postmark system on Dec. 24, 2025, defining the postmark as the date of the first automated processing, which may differ from the drop-off date. This impacts tax filings because documents must bear a postmark on or before the due date to be considered timely under IRC Sec. 7502. To ensure compliance, taxpayers should request a manual postmark at a USPS retail counter or use Registered/Certified Mail for proof of mailing.