USPS Announces Changes to the Postmark Date System
nstp.org
The United States Postal Service (USPS) has adopted a final rule (FR Doc.

A Bluesky post

USPS changed policy on when they postmark mail. Mail dropped off is no longer guaranteed a same-day postmark. Tax returns & other time-sensitive items are now stamped when they reach a regional processing center, which may be days later. Plan deadlines accordingly to avoid penalties.