(a) A corporation's registered agent is the corporation's agent for service of process, notice, or demand required or permitted by law to be served on the corporation.
(b) If a corporation has no registered agent, or the agent cannot with reasonable diligence be served, the corporation may be served by registered or certified mail, return receipt requested, addressed to the secretary of the corporation at its principal office shown in the most recent biennial report filed pursuant to section 21-19,172. Service is perfected under this subsection on the earliest of:
(1) The date the corporation receives the mail;
(2) The date shown on the return receipt, if signed on behalf of the corporation; or
(3) Five days after its deposit in the United States mail, if mailed and correctly addressed with first-class postage affixed.
(c) This section does not prescribe the only means, or necessarily the required means, of serving a corporation.