Could not send mail to users email using my smtp server on website

Question

My goal is sending mail from smtp server on my website (lets say: example.com) to user (lets say: [email protected]).

What I have done

I created SMTP server on my website using nodejs module "smtp-server" and tested it by sending mail from [email protected] to [email protected] successfully by referring to website: https://simonjcarr.medium.com/create-an-smtp-server-with-nodejs-5688d8fd882e. code for my server is attached below

const SMTPServer = require("smtp-server").SMTPServer;
const parser = require("mailparser").simpleParser

const server = new SMTPServer({
    onData(stream, session, callback) {
        parser(stream, {}, (err, parsed) => {
          if (err){
            console.log("Error:" , err);
            return callback(new Error("Error occured"));
          }
          
          console.log(parsed)
          stream.on("end", callback)
          return callback(); // Accept the connection
        })
        
      },
      disabledCommands: ['AUTH'],
});

server.listen(25 ,() => {
    console.log("Email Server is on.")
});

What I tried

I tried sending mail from my laptop to "[email protected]" using code written using "nodemailer" for which I referred https://nodemailer.com/about/. I assumed that if I mention gmail account in "to" option and my server in "host" and run command from my laptop then my mail will be sent to [email protected] via my SMTP server on example.com. The code I used for sending mail is as below:

var nodemailer = require('nodemailer');

const transporter = nodemailer.createTransport({
    port: 25, // Postfix uses port 25
    host: 'mail.example.com',
    tls: {
      rejectUnauthorized: false
    },
    secure: false,
  });
  
  var message = {
    from: '[email protected]',
    to: '[email protected]',
    subject: 'Confirm Email',
    text: 'Please confirm your email',
    html: '<p>Please confirm your email</p>'
  };
  
  transporter.sendMail(message, (error, info) => {
    if (error) {
        return console.log(error);
    }
    console.log('Message sent: %s', info.messageId);
  });

Result

However, when I run this code I get response on my SMTP server but mail never reaches gmail account. Kindly help me making it work.