Sending email from own server to the internets

I have set up an email server on my host. It's basically a SMTP server that listens on port 25.

const recvServer = new SMTPServer({
  requireTLS: true,
  authOptional: true,
  logger: true,      
  onConnect(session, callback) {
    return callback();
  },

  onMailFrom(address, session, callback) {
    console.log('from', address, session);
    return callback();
  },    

  onData(stream, session, callback) {
    console.log('new msg');
    let message = '';
    stream.on('data', chunk => {
      message += chunk;
    });

    stream.on('end', () => {

      callback(null, 'Message queued');
      simpleParser(message)
        .then(parsed => {
          console.log(parsed);
          // here I wish to forward the message to outside gmail addresses
        })
        .catch(err => {
          console.log(ee)
        });

    });
  }    
});

recvServer.listen(25);

recvServer.on('error', err => {
  console.log(err.message);
});

It works fine for receiving emails from outside, like gmail etc.

But I want to be able to send emails outside also, or forward emails that I receive to some gmail addresses.

I know that I can do that using Gmail SMTP servers, but then I need an gmail account and password.

I want to be able to send email with my own server, just like yahoo sends mail to gmail using their own server not gmail accounts :)

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