In December 2025, the US Postal Service rolled out Rule 608.11. This new rule is a gamechanger for individuals who require timely-filed mail delivered by the Postal Service. These individuals include individual taxpayers who file their annual tax returns and other related tax documents such as estimated tax payments using US mail.
Effective January 1, 2026, first class mail is now postmarked when it is processed at a regional enter, which could be days after being received by the post office. A delayed postmark could be especially detrimental for those individuals who mail Their federal and state income tax returns via regular mail. Delayed receipt of income tax returns could lead to late filing penalties, interest or even missed claims. Professional tax advisors are recommending that individuals take steps to ensure enhanced proof of timely mailings.
This column discusses what federal employees and retirees should know about how the new Postal Service rule affects proof of timely mailings. Moreover, for those federal employees and retirees who prepare their own federal and state income tax returns, the steps they need to take to avoid penalties, interest and late claims for last-minute filing by mail.
What is the IRS “Mailbox Rule” and How Does It Affect Mailed Income Tax Returns?
The “mailbox rule” (contained in Internal Revenue Code Section 7502) specifies that a mailed tax return is timely if it is postmarked by the income tax due date. This means that a postmark governs any dispute whether or not a tax return is filed in a timely fashion. In the past, a postmark for first class mail generally reflected the day an income tax return was mailed.
However, in recent years the Postal Service has changed the rules resulting in the postmark being the date when a mailing is processed and not necessarily when it is formally mailed. This USPS change in operations is due to automation, cost-cutting and regional processing. Regional processing centers are now where mail is frequently processed.
In addition, a delayed postmark may result in an item being mailed after the last pickup of the day, or a post office with limited pickups.
The result of these changes and delayed postmarks is that unless Congress changes the Internal Revenue Code or the IRS issues some relief guidance (both highly unlikely), a postmark after the due date from this new Postal Service rule will most likely result in many individuals paying IRS late filing penalties and interest charges.
The upshot of the new Postal Service rule is that individuals and businesses cannot rely on the IRS’ receipt of documents mailed near or on a due date. This is because the Postal Service now frequently fails to deliver mail received in any kind in a timely fashion. Under IRC Section 7502, a late postmark will cause a deemed late filing or a late payment. It is therefore correct to assume that because of existing delays in mail delivery, the IRS will probably increase postmark checks.
What Can Individuals Do to Ensure Proof of Timely Income Tax Return Filing?
There are some actions that individuals can take to make sure that their 2025 federal and state income tax returns are postmarked in a timely fashion.
1. Individuals should not mail the return via a mailbox. They should go in-person to a post office with their mailings. The best and safest method (as established by many court decisions) is to obtain conclusive proof of the mailing date. In particular, sending the tax return Certified Mail with return receipt requested, with the receipt’s date stamped at the post office. An alternative is that the individual mailing the tax return should purchase postage that the post office prints and affixes to the mailing with the date of mailing shown or request a hand-canceled postmark. Stamps individually purchased should not be used.
2. Mail the income tax return using a private delivery service, such as Federal Express, UPS or DHL. These private delivery services are more expensive than the Postal Service. The more expensive services may provide more services and may not have long customer lines. Note that there are specific US Treasury regulations to be complied with when a private delivery service is used to mail a federal income tax return.
3. Electronically file the income tax return using direct debit to pay any balance due. While electronic filing is commonly used, some individuals wish to retain cash in their account until the IRS processes a physical check, or they may have other reasons not to want the IRS or state revenue department to have access to their account information. New IRS regulations seriously restrict use of paper checks. As of September 30, 2025, the Treasury Department no longer issues paper checks.
Finally, individuals should be aware that commonly used mechanisms to indicate date of mailing will not work with the new Postal Service rule. That includes preprinted labels supplied by a mail customer before mailing (such as postage from self-service kiosks or meter strips) are ineffective to either confirm the acceptance of the mail by the Postal Service or the specific date on which such acceptance occurs.
Individuals are reminded to retain receipts or other proof of timely mail when mailing their income tax returns.