Due to changes in the US Postal Service, mail can no longer be guaranteed to be postmarked on the day it is collected. The US Postal Service has stated that it can now take up to 3-4 days for regularly collected mail to be postmarked. It is recommended that anyone mailing in tax payments close to the due dates to hand the letter to the postal worker behind the counter, and they can stamp it with the postmarked date. Doing this will prevent tax bills from being considered late and incurring extra costs and payments. Read more.