When is it appropriate to use static (over unnamed namespaces) in C++?

I have been reading articles about unnamed namespaces the whole day, most articles explained when you should use unnamed namespaces over the static keyword. But I am still left with one big question when is it appropriate to use static? After all it is not completely deprecated, what about header files with static functions should I put them into unnamed namespaces now?

#ifndef HEADER_H
#define HEADER_H

static int func() {

  ...
}

// versus:

namespace {
  int func() {
    ...
  }
};


#endif // HEADER_H 

Or what about static member functions?

Greetings