Legal Question in Real Estate Law in California

There is no such thing as a "courier server." If you mean process server, anyone mentally competent and over the age of 18 who does not have a legal interest in the outcome of the case can serve process. So a spouse generally cannot, and of course a party to the case cannot, but a friend, relative, neighbor, etc., all can do it legally. If it is done for pay, however, the person must be a registered process server.