Tex. Elec. Code § 1.008
When this code requires an application, notice, report, or other document or paper to be delivered, submitted, or filed within a specified period or before a specified deadline, a delivery, submission, or filing by first-class United States mail is timely, except as otherwise provided by this code, if:
Acts 1985, 69th Leg., ch. 211, Sec. 1, eff. Jan. 1, 1986.