def tos_from(to)
        case to
        when String
          { to => {} }
        when Array
          to.map { |single_to| [single_to, {}] }.to_h
        when Hash
          to
        else
          to.to_h
        end
      end
def tos_from(to)
        case to
        when String
          { to => {} }
        when Array
          to.map { |single_to| [single_to, {}] }.to_h
        when Hash
          to
        else
          to.to_h
        end
      end
HELPER METHODS 
 @return [Hash]
   p.e. { 'some@mail.ch' => { a_variable: 'Hello' } }