The video above shows the bags pulled out of the car surrounded by mail.
The driver was also intoxicated behind the wheel when he was stopped by Deputy Parrella at the Katy Freeway and Grand Parkway, according to a tweet by the sheriff's office.
Mail theft is a felony under federal law.
There was no word on the identity of the driver.
District 4 Deputy Parrella made a traffic stop. Driver was DWI. In the vehicle a large quantity of undelivered US Mail was located. US Postal inspectors have begun a federal investigation into the stolen mail. @HCSOTexas @SheriffEd_HCSO @HCSOPatrol @HCSO_D4Patrol pic.twitter.com/mjt6WRD7IQ— Captain J. Shannon (@HCSO_NightShift) August 29, 2020