Nebraska Revised Statute 21-236
Service on corporation.
(MBCA 5.04) (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. Service is perfected under this subsection at 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, as evidenced by the postmark, if mailed postpaid and correctly addressed.
(c) This section does not prescribe the only means, or necessarily the required means, of serving a corporation.