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Because of changes to how the U.S. Postal Service (USPS) treats postmarks on First Class mail, taxpayers face increased risks of mailed tax returns and payments being deemed late.
Grant Thornton insight:
To avoid this potential foot fault, best practice is to always instruct clients to use USPS Registered Mail or USPS Certified Mail (Return Receipt Requested) or an IRS-designated private delivery service.
Effective Dec. 24, 2025, the USPS redefined what constitutes a postmark, where postmarks may be applied, how postmarks correspond to dates of acceptance, and which services establish proof of the date of acceptance.
The new regulations note that a postmark is a marking applied by the USPS to a mail piece and may be applied on the date that the first automated processing operation is performed on the mailed item. The issue arises with ordinary First Class mail, because the postmark may reflect a later date than that when the USPS first accepts the item. This can result from USPS processing issues and the movement of mail into and out of processing facilities.
The IRS’ “Mailbox Rule” in Section 7502 provides that the date of the USPS postmark on the envelope of a mailed item is deemed the date on which the IRS received the item. Section 7502 further provides that an item mailed using USPS Registered Mail or USPS Certified Mail, or by a designated private delivery service, constitutes prima facie evidence that the IRS received the item on the date shown on the postmark.
However, when First Class mail is used to submit any return, claim, statement, payment or other document to the IRS, a taxpayer risks the item receiving a postmark date that is later than the date USPS first accepts the item. For this reason, taxpayers are encouraged to file and pay electronically or use USPS Registered Mail, USPS Certified Mail (with Return Receipt Requested) or an IRS-designated private delivery service.
In addition to using one of these recommended methods for any documents clients must mail to the IRS, clients also can obtain one of the following proofs of acceptance at the post office:
- A manual postmark to be applied to the mail piece at the time of acceptance;
- A postage validation imprint (PVI) label showing the date USPS accepted the item; or
- A certificate of mailing, which must be purchased, showing the date the item was mailed.
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