docs: private static boolean _hasMXRecord (@Nonnull final String sHostName)
    {
      try
      {
        final Record [] aRecords = new Lookup (sHostName, Type.MX).run ();
        return aRecords != null && aRecords.length > 0;
      }
      catch (final Exception ex)
      {
        // Do not log this message, as this method is potentially called very
        // often!
        if (LOGGER.isWarnEnabled ())
          LOGGER.warn ("Failed to check for MX record on host '" +
                          sHostName +
                          "': " +
                          ex.getClass ().getName () +
                          " - " +
                          ex.getMessage ());
        return false;
      }
    }