The restraining order could be served by publication since your estranged husband's whereabouts are unknown.  Service by publication is having it appear in the legal notices section of a newspaper.  Check with the court clerk and ask how long the notice has to run in the newspaper for it to be effective service by publication.  It used to be four weeks, but you should confirm that with the court clerk in case it has changed.  Even if your estranged husband does not see the notice in the newspaper, it is still effective service of process.