def domains
      @_domains ||= mxers.map {|m| EmailAddress::Host.new(m.first).domain_name }.sort.uniq
    end
def domains
      @_domains ||= mxers.map {|m| EmailAddress::Host.new(m.first).domain_name }.sort.uniq
    end
Returns Array of domain names for the MX'ers, used to determine the Provider