12/11/2025
The USPS has instituted a new rule stating that postmarks are only applied at the first automation step, not at the time of acceptance. This means that when you put an envelope in your mailbox, it won't be postmarked until it arrives at a sorting center up to a few days later. Missouri law currently relies on the postmark date to determine if late fees are applied to tax payments. To avoid late fees, please do not wait until the last few days of December to mail your payment. To be extra certain, consider mailing your payment at a post office location and have a clerk manually postmark it, or use a mail class like Certified, Registered, or Priority and save your receipt with the acceptance date.