From page 5137 of HOUSE AMENDMENT TO THE SENATE AMENDMENT TO H.R. 133 which is part of the 2020 Omnibus Bill

SEC. 603. NON MAILABILITY OF ELECTRONIC NICOTINE DELIVERY SYSTEMS. 

(a) REGULATIONS.—Not later than 120 days after the date of enactment of this Act, the United States Postal Service shall promulgate regulations to clarify the applicability of the prohibition on mailing of cigarettes under section 1716E of title 18, United States Code, to electronic nicotine delivery systems, in accordance with the amendment to the definition of ‘‘cigarette’’ made by section 602. 

(b) EFFECTIVE DATE.—The prohibition on mailing of cigarettes under section 1716E of title 18, United States Code, shall apply to electronic nicotine delivery systems on and after the date on which the United States Postal Service promulgates regulations under subsection (a) of this section. 

We can still use UPS, FedEX and DHL 🙂