Risk Alert: New Post Office Rule Affects (Delays) Postmark Date for First Class Mail

By Kenneth M. Horwitz, J.D., LL.M.(Tax), CPA-Dallas, Member, Glast Phillips Murray Zopolsky; and William Stromsem, J.D., CPA, George Washington University School of Business

At the end of December 2025, the U.S. Postal Service seriously degraded First Class mail by implementing a new rule (Rule 608.11) for postmark dates, generally adversely delaying the postmark date. Previously, First Class mail was postmarked by the local post office on the date accepted by that local post office.

You and your clients should be aware of how the rule affects proof of timely mailing and the steps to take to avoid penalties, interest and late claims for last-minute mailings. Failure to take appropriate steps as discussed below could well lead to claims for damages by clients.

The “mailbox rule” in Section 7502 of the Internal Revenue Code (IRC) specifies that a mailing is timely if it is postmarked by the due date, so the postmark governs any dispute as to timely mailing. In the past, the postmark for First Class mail generally reflected the day an item was mailed (that is, received by the local post office). However, with automation, cost-cutting and regional processing, the USPS has changed the rule so that the postmark will now be the date when the mailing is processed (frequently at a regional processing center), not necessarily when it is mailed. This can mean that a timely-mailed item may be postmarked one, two or more days after it is mailed. A further delayed postmark may result if an item is mailed after the last pickup for the day or at a post office with limited pickups. Unless Congress changes the IRC or the IRS issues some relief guidance (neither of which is likely), a postmark after the due date resulting from this new USPS rule that degrades service (and that potentially may violate the mailbox rule) may well, depending on the content of the mailing, result in penalties and interest or, for example, a late filed claim because of the statute of limitations (and serious financial harm to the client).

You cannot rely on the IRS receiving documents mailed near or on a due date because the USPS frequently now fails to deliver mail received in any kind of timely fashion. While it is true that the IRS has historically not checked mail received close to a due date, it would be pure folly to rely on such IRS practice to avoid penalties, interest and worse. A late postmark causes a deemed late filing or a late payment under IRC Section 7502. You should assume that because of existing delays in mail delivery, the IRS will probably increase postmark checks.

There are some steps that can be taken to ensure enhanced proof of timely mailing, many of which are already being used by savvy practitioners.

1. Visit the post office with the mailing. (A) the best, safest method, as established by many court decisions, that is conclusive proof of mailing date is to send mail Certified Mail, Return Receipt Requested, white receipt date-stamped at the post office and retained in the practitioner’s file with a copy of the mailed document; or (B) purchase postage that the post office prints and affixes to the mailing with the mailing date or request a hand-canceled postmark. Neither of these costs extra, although you may need to wait in line. You could also buy upgraded USPS services, like a Certificate of Mailing or certified (see (A) above) or registered mail (certified is less expensive). NOTE: You will be required to contact the local post office in advance to arrange if 50 or more pieces of mail will be presented for manual postmark application (to ensure that adequate postal resources are available).

2. Take your item to a private delivery service, such as FedEx, UPS or DHL. These are generally more expensive than postal service, but may provide more service and may not have long customer lines, noting that there are specific Treasury Regulations to be complied with if you use such private delivery services.

3. E-pay with an electronically filed return. This is commonly used, but some clients 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 to have access to their account information. (New IRS regulations seriously restrict use of paper checks.)

Commonly used mechanisms to indicate date of mailing simply do not work under this new Postal rule. Thus, 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 USPS or the specific date on which such acceptance occurs.

In all cases, be sure to retain receipts or other proof of timely mailing.

See: Establishing Proof of Timely Mailing Under the IRS Mailbox Rule

See: USPS postmark changes create new filing risks for tax pros | NATP