USPS mail processing changes may delay postmarking and redefine timely mailing. This alert outlines the professional liability risks for CPAs and steps to mitigate them.
By CNA Accountants Risk Control
Recent USPS regulations clarified that mail dropped at a local post office or placed in a collection box may not receive a postmark until it reaches a regional processing center — often a day or more after deposit. This creates significant potential compliance risk for both taxpayers and CPAs who rely on postmarks to substantiate timely filings for tax compliance obligations and other legal purposes.
This risk alert is intended for CPAs, tax preparers, and accounting professionals who rely on, or whose clients rely on, postmarks as evidence of timely mailing.
How has USPS clarified application of postmarks?
Effective December 24, 2025, USPS formally added Section 608.11 (“Postmarks and Postal Possession”) to the Domestic Mail Manual, defining what constitutes a postmark and clarifying when USPS applies one in the mail delivery process. The new rule explains that a mailpiece is not postmarked when it is handed to a clerk, dropped into a blue collection box, or deposited at a retail post office lobby. Instead, most postmarks are applied only when the mailpiece undergoes automated processing at a USPS processing facility.
USPS notes that the rule does not change existing operations; automated machines at processing facilities have applied most postmarks for decades.
How does this affect me and my clients?
Because postmarks reflect the date a mailpiece is processed regionally rather than when it was deposited locally, traditional assumptions about “mail by the deadline” are no longer correct. Nearly half of all U.S. post offices are more than 100 miles from their processing center, meaning mail may not receive a postmark until one or more days after receipt by USPS. Consequently, if returns are dropped at a local post office on or shortly before a tax filing deadline, they may not be postmarked until days later, potentially after the deadline.
Furthermore, these changes affect scenarios beyond annual tax return obligations, including communications with regulatory authorities, quarterly payments, and Tax Court petitions, among others.
What are the professional liability risks to CPAs?
Postmarks after the due date alter how tax authorities and courts evaluate timely mailing. Under Internal Revenue Code Section 7502 (commonly referred to as the “mailbox rule”), timely mailing is treated as timely filing — but only if the postmark shows a date on or before the deadline. If a filing is dropped off on the due date but not processed — and therefore not postmarked — until the next day, the filing will be deemed late.
Real-world consequences for CPAs could include professional liability claims arising from:
- Tax filings and payments: Tax returns or payments being considered late even if mailed on the due date, increasing exposure to late filing penalties, interest, and missed elections.
- Regulatory authority communications: Communications with legally defined deadlines, such as notice responses, Information Document Requests, or subpoenas, will be rejected for lateness if the postmark date does not align with the mandated deadline.
- Tax Court petitions: A late postmark will cause dismissal of a petition, as taxpayers must petition the Tax Court within 90 days of the notice of deficiency. Courts have historically upheld postmark evidence when assessing whether petitions were timely filed.
These risks are especially acute in rural areas, where mail may travel long distances before reaching a regional processing center and receive a postmark several days after being deposited at a post office. CPAs serving rural clients may want to take particular care to avoid inadvertent late filings.
What can CPAs do to address these risks?
To reduce filing and compliance risk, it is recommended that CPA firms review and update their procedures to reflect the new USPS postmark guidance. The following steps can help provide evidence of timely mailing and help protect accounting firms and their clients from penalties and interest, rejected filings, missed elections, and resulting litigation exposure.
Adjust internal protocols
Consider updating internal protocols to avoid last-minute mailings where possible. This may include:
- Moving internal deadlines earlier, especially for clients who historically have filed paper returns or will pay balances due with paper checks.
- Encouraging the use of electronic filing where available and documenting client approval with Form 8879.
- Developing standard procedures for obtaining appropriate proof of mailing and communicating these procedures to all involved in tax return preparation and filing.
Understand options for obtaining proof of mailing
Proof of mailing and receipt
Certified Mail Return Receipt Requested and Certificate of Mailing are the most thorough options available because these services document both proof of mailing to and confirmation of receipt by the taxing authority.
Proof of mailing
The following methods evidence proof of mailing only:
- A free manual postmark applied at the local post office retail counter
- Postage Validation Imprint (PVI) labels, which indicate the postage paid and the date on which the mailpiece was accepted at the local post office
- Registered Mail
While these methods help document the date mailed, proof of mailing alone does nothing if the IRS doesn’t receive your tax return.
Client notification
Consider notifying all clients of the clarifications to USPS postmarking procedures, including a description of the various methods by which postmarks can be applied and applicable links for more information. If this message is sent via a newsletter, client alert, or similar communication, retain copies of the communication and the distribution list.
If you have clients that you know file their own paper returns or do not electronically remit IRS payments, consider notifying these clients individually of their responsibility for obtaining the appropriate postmark to evidence timely filing and payment.
In addition, to account for potential processing delays, encourage clients to:
- File electronically where permitted.
- Send time-sensitive documents which cannot be filed electronically several days early, especially during high-volume times like tax season.
- Utilize Certified Mail Return Receipt Requested or Certificate of Mailing to document timely mailing to and receipt by the taxing authority.
- Transition to electronic payment methods rather than paper checks; see the Risk Alert on mandatory electronic payments for further information on this topic.
If engagement letters have not yet been sent, CPAs may also consider adding a provision to their engagement letters and filing instructions re-iterating that traditional assumptions about “mail by the deadline” are no longer correct. A sample provision follows:
Recent USPS regulations clarified that mail dropped at a local post office or placed in a collection box may not receive a postmark until it reaches a regional processing center — often a day or more after deposit. If you choose to file your own paper return(s) and/or remit payment by paper check, you are responsible for obtaining the appropriate postmark to evidence timely filing and/or payment.
In conclusion
Although clients are ultimately responsible for their tax compliance obligations, changes to USPS postmarking procedures represent a significant risk to CPAs and may lead to missed deadlines and future claims. Proactive communication and thoughtful planning can help.
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