Is the tax return considered timely filed if received on the day it was postmarked or the day the IRS received it ?

A tax return delivered to the IRS by U.S. mail after the due date is considered timely filed if the return was postmarked on or before the due date of the return. This rule includes postmarks supplied by any private delivery service designated by the Service. An income tax return postmarked April 15 and received by the IRS on April 19 is considered timely filed.