Effective December 24, 2025, the United States Postal Service (USPS) adopted final rules that revise how postmarks are defined and treated. These changes have important implications for taxpayers who plan to mail their tax returns and rely on postmarks to establish timely filing.
Under the new framework, the USPS has clarified and, in some cases, narrowed what qualifies as an official postmark, where and when postmarks may be applied, how postmark dates correspond to the USPS’s acceptance of a mailpiece, and which mailing methods provide valid evidence of mailing dates. Taxpayers who do not adhere to the updated requirements may face an increased risk that their returns will be treated as late‑filed.
The USPS finalized the newly added Section 608.11, “Postmarks and Postal Possession” (the Final Rule), as part of the Domestic Mail Manual. On August 12, 2025, the USPS published the proposed rule, 90 F.R. 38716, and invited public comment. The USPS noted that this process was not a traditional rulemaking process because the Final Rule does not make any changes to USPS procedures for applying postmarks to mail and instead provides key definitions. The Final Rule’s purpose is to document existing practices and provide clearer guidance on how postmarks work and how they may differ from a mailpiece’s actual date of mailing.
What is the Final Rule?
Under the Final Rule, a “postmark” is defined as a marking applied by the USPS to confirm its acceptance of custody of a mailpiece. The postmark displays the location of the processing facility or retail unit that applied it, which may not be the location where the USPS first obtained possession of the mailpiece. As a result, the postmark date is not necessarily the date the USPS first obtained possession of the mailpiece. The postmark date generally reflects either the date of the first automated processing operation that is performed on the mailpiece or the date that the mailpiece was first accepted at a retail counter. Because most postmarks are applied at processing facilities, the postmark date and location often differ from the date and place of initial acceptance of the mailpiece
On January 2, 2026, the USPS issued a public statement titled Postmarking Myths and Facts, reiterating that it has not changed its postmarking practices. However, the USPS explained that recent adjustments to its transportation network mean some mail may not reach the processing facility on the same day it is collected or dropped off. Consequently, the postmark date applied at a processing center may differ from the actual date the customer mailed the item.
The Final Rule aims to equip customers with enough information to adjust their mailing practices (e.g., by mailing earlier, requesting a manual postmark at a retail location, or purchasing a Certificate of Mailing).
Importance for tax filings
Internal Revenue Code Section 7502(a) provides that the postmark date is treated as the date a tax return or payment is delivered to the Internal Revenue Service (IRS), sometimes known as the [...]
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