01/07/26
News
USPS Clarifies ‘Delayed’ Postmarking and Potential Late Fees and Penalties on Mail-in Returns, IRS Correspondence
5 Min Read
Key Takeaways
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A recent clarification from the U.S. Postal Service (USPS) highlights something many taxpayers may not realize: the date stamped on a piece of mail isn’t always the day it was sent. This “delayed” postmarking may have implications in certain scenarios, particularly for manually-filed tax returns, extension requests, and IRS correspondence where even a one-day delay can trigger penalties or interest.
The leaders of our Tax Practice explain why this could cause problems during tax filing and how to mitigate the potential for issues with the mail.
Clarification on postmarking
Postmarking has commonly been viewed as proof of when mail was sent, but the USPS recently clarified that most postmarks are applied automatically at processing facilities, not necessarily at the moment a customer hands an envelope to a postal clerk or drops it in a collection box, which could be one or two days later. The discrepancy comes as a result of operational changes introduced in 2021 with the Delivering for America initiative which brought changes to transportation schedules and a decrease in the frequency that processing hubs receive mail in a day.
A document placed in the mail on April 15, for example, could receive a postmark dated April 16 if it does not enter automated processing at a mail facility until the following day.
This distinction is especially important for tax filings and payments mailed to the IRS, where deadlines are strict and late submissions can result in penalties, interest, or other consequences.
Impact on IRS filings and payments
The IRS generally treats the U.S. postmark date as the official filing date for returns and other documents sent by mail. If that postmark reflects a date after the deadline, even if the taxpayer mailed the item on time, the IRS may consider the filing late.
This risk extends beyond individual income tax returns. Businesses that mail payroll tax forms, partnership and S corporation returns, extension requests, estimated tax payments, and other compliance documents face similar exposure. The same is true for correspondence related to audits, notices, or disputes where response deadlines apply.
In addition, many non-tax obligations rely on postmark dates, including payments to state agencies, courts, and other entities where late fees or penalties can accrue.
Steps to reduce risk when mailing time-sensitive documents
Whenever possible, taxpayers should prioritize electronic filing and payment options, which provide immediate confirmation and eliminate the uncertainty associated with postmarks entirely. E-filing returns and submitting payments electronically is the most reliable way to meet IRS deadlines and avoid disputes over timing.
For situations where mailing documents is unavoidable, taxpayers should take additional precautions to protect themselves:
- Mail early when possible
Avoid sending time-sensitive documents on the filing deadline. Mailing even one or two days early can help reduce the risk of delayed postmarking during USPS processing. - Certified Mail with return receipt
Certified Mail offers documented proof of mailing and delivery and is widely accepted as evidence of timely filing by the IRS. - Request a manual postmark
When feasible, present the mail piece to a USPS retail counter employee and request a manual postmark. This helps ensure the postmark reflects the actual date the item was submitted. - Use USPS retail postage validation
Purchasing postage at a USPS retail counter and retaining the dated receipt can provide additional support if the timing of a filing is ever questioned.
Bottom line
The USPS clarification does not change tax law, but it does highlight a practical risk for anyone relying on the mail to meet filing deadlines. With penalties and interest often triggered automatically, taxpayers and businesses should reassess how and when they send time-sensitive documents.
With the 2026 tax filing season on the horizon, now is a good time to review how deadlines are determined. Start preparing for tax filing today to avoid the risks of delays or problems with mailed-in tax forms or correspondence.
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Author
LONI WINKLER
Partner, UHY LLP Managing Director, UHY Advisors
Loni Winkler is the leader of the tax practice in the Great Lakes region and has over 20 years of experience in public accounting. She provides tax and business consulting services to privately held businesses and has extensive experience in individual, corporate and flow-through entity federal and multi-state taxations. She assists business owners, CFOs and controllers in developing and implementing innovative business strategies to minimize risk, maximize profits, preserve wealth, and reduce taxes.