Effective December 24, 2025, the United States Postal Service has implemented changes that may affect the postmark date, and that date may now be later than the date an item is dropped in the mail. Because tax deadlines are based on the postmark date, mailing close to a deadline may result in a late postmark. Obtaining proof of mailing, such as a manual USPS postmark obtained at a retail counter, Certificate of Mailing; or sending by Certified Mail, Registered Mail, or another IRS-approved delivery service that provides documented proof of mailing date, can help reduce this risk.