# File lib/action_mailer/vendor/tmail-1.2.3/tmail/net.rb, line 96
    def mime_encode_singlepart
      self.mime_version = '1.0'
      b = body
      if NKF.guess(b) != NKF::BINARY
        mime_encode_text b
      else
        mime_encode_binary b
      end
    end