January 24, 2026 - A new U.S. Postal Service rule Section 608.11 could impact when time-sensitive mail, such as tax forms and tax payments, is considered officially sent. Effective Dec. 24, 2025, mailed items are postmarked when the USPS processes them, rather than the date items are dropped in a mailbox or at a post office. A postmark refers to the date and location stamped or printed on most mailed items, indicating when and where the USPS “accepted custody” of a mail piece, according to the federal agency. The USPS said its Dec.