All business done in this State by insurers doing the business of insurance as defined in this title must be transacted by their regularly authorized agents licensed in this State or through applications of the agents. Except as provided in Section 38-43-70, it is unlawful for a salaried officer, manager, or other representative of an insurer to transact for his company any of the business of a licensed agent for which the licensed agent received a commission, unless he himself is a bona fide licensed agent. No provision of this section applies to direct insurance covering the rolling stock of railroad corporations or property in transit while in possession and custody of railroad corporations or other common carriers or applies to bid bonds issued by a surety insurer in connection with any public or private contract.