Email OTP Verification System Without Using Any Extension

Hello I want the mail.php script

function doPost(e) {
var recipient = e.parameters.recipient;
    recipient = decodeURI(recipient);
var subject = e.parameters.subject;
    subject = decodeURI(subject);
var body = e.parameters.body;
    body = decodeURI(body);

  MailApp.sendEmail(recipient, subject, body );
}

Nice Application. Could use it to send OTP