The U.S. Postal Service issued final regulations effective December 24, 2025, clarifying how postmarks are applied and why the date shown may not reflect the day a document was mailed. While the concept of postmarking itself is not new, recent operational changes at the USPS could result in the postmarks that are applied to an envelope or package be up to a week later than when you dropped the envelope or package at your local post office.
For taxpayers and businesses that rely on the timely mailed timely filed rule, this shift introduces new risks that require more deliberate planning.
Why This Matters for Tax Filings
Federal tax rules rely heavily on the postmark date to determine whether filings and payments are made promptly. When the postmark date controls, mailing an envelope or package on time no longer guarantees that the postmark will reflect timely compliance.
The risks extend to several ordinary tax-related submissions:
- Estimated Tax Payments
- Tax return deadlines may be missed if the postmark date falls after the due date, even if the return was mailed earlier
- Estimated tax payments may be treated as late, resulting in penalties
- IRS correspondence, elections, and appeals could be deemed untimely
- Charitable contribution documentation for year-end giving may be compromised
In effect, the burden of proof has shifted more heavily to the sender.
How Businesses Can Reduce Mailing Risk
Given the increased uncertainty around postmarks, businesses and individuals should take extra precautions when mailing time-sensitive documents:
- Use Certified or Registered Mail to obtain a postmarked receipt
- Use Certificate of Mailing issued by the Post Office
- Use IRS-approved private delivery services when appropriate
Electronic submission eliminates the uncertainty of postmarking and may be the safest option for filings tied to strict deadlines.
Considerations for Business Owners
Mailing deadlines leave little room for assumption. Changes in USPS processing mean that dropping mail in a box on the due date may no longer provide adequate protection.
Being intentional about how and where time-sensitive tax documents are mailed can help reduce risk and avoid unnecessary penalties. If you have questions about the safest mailing or filing options for tax documents, your tax advisor can help you evaluate the best approach based on your specific situation.