nodemailer Error: self signed certificate in certificate chain

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var transporter = nodemailer.createTransport({
      host: "outmail.abc.co.th", // hostname
      secure: false, // use SSL
      port: 25, // port for secure SMTP
      auth: {
          user: "[email protected]",
          pass: "passwordmail"
      },
      tls: {
          rejectUnauthorized: false
      }
  });