Okla. Stat. tit. 74 § 76
The Office of Management and Enterprise Services is authorized to initiate and operate a mailing service for the agencies and departments of the state located in Oklahoma City. The Director of the Office of Management and Enterprise Services shall promulgate and adopt such reasonable rules and regulations as may be necessary for the efficient and economical operation of a clearinghouse for interagency communications and for the deposit of the state's mail with the United States Post Office. The Office shall have the authority to employ such personnel and to purchase and acquire such equipment, materials, and supplies as may be necessary to carry out the provisions of Sections 76 through 76b of this title. Every agency and department of the state located in Oklahoma City shall be required to participate in the mailing service, except the Department of Human Services, the Commission for Human Services, the Oklahoma Tax Commission, the University of Oklahoma Medical Center, the Oklahoma Employment Security Commission, the Oklahoma Legislature, the Oklahoma Medical Center, and the State Department of Health located in the Oklahoma Health Sciences Center.
Okla. Stat. tit. 74, § 76