(a) If a public official is required or permitted by law to serve legal process by mail, including process in a suit for delinquent taxes, the official may:
(1) collect advance payment for the actual cost of the postage required to serve or deliver the process; or
(2) assess the expense of postage as costs.
(b) Charges under this section are in addition to other charges allowed by law for services performed by the official serving the process.