Mailgun - Unauthenticated email from guest.com - node.js

Question

I have mailgun setup in my node.js using nodemailer and I cannot get it to send emails when I test my route using my REST client. When I directly write the code into the server file, the email sends right away when the server starts.
However, when I write the email api in an app.post and test it with a REST client the email fails on the mailgun side and gets rejected by google??? This is only my assumption because of the error code I am getting.
Server response: 550 5.7.1 Unauthenticated email from guest.com is not
accepted due to domain's 5.7.1 DMARC policy. Please contact the administrator
of guest.com domain if 5.7.1 this was a legitimate mail. Please visit 5.7.1
https://support.google.com/mail/answer/2451690 to learn about the 5.7.1 DMARC
initiative. s12-v6si3013316qtg.362 - gsmtp
I've followed the link provided and the documentation says to check with the domain server. I do not understand why I am getting this error because I already authenticated my gmail within mailgun.
I've also tried switching to directly using the mailgun-js middleware. Found three different mailgun-js api from mailgun.com, mailgun-js on github, and mailgun-js on npmjs.com. Got the same error as above.
At a loss. Don't know what to do.
My nodemailer code:
const express = require('express');
const nodemailer = require('nodemailer');
const path = require('path');
const bodyParser = require('body-parser');
const app = express();
const port = 3000;
app.use(bodyParser.json());
app.use(express.static(path.join(__dirname, 'dist')));
app.post('/email', (req, res) => {
let transporter = nodemailer.createTransport({
host: 'smtp.mailgun.org',
port: 587,
secure: false, // true for 465, false for other ports
auth: {
user: 'postmaster#sandboxc8f2ecf64f364ca6ad740e658485c557.mailgun.org',
pass: 'my API key here'
},
tls: {
rejectUnauthorized: false
}
});
// setup email data with unicode symbols
let mailOptions = {
from: req.body.from, // sender address
to: 'cu0ngpitt#gmail.com', // list of receivers
subject: 'Someone wrote you from your Online Resume!', // Subject line
text: req.body.messge, // plain text body
};
// send mail with defined transport object
transporter.sendMail(mailOptions, (error, info) => {
if (error) {
return console.log(error);
}
console.log('Message sent: %s', info.messageId);
console.log('Preview URL: %s', nodemailer.getTestMessageUrl(info));
});
});
app.get('/', (req, res) => {
res.send('Hello world');
});
app.listen(port, () => {
console.log('Server running on port ' + port);
})

Answer 1

Mailgun responded to my ticket and said due to DMARC security, I am only allowed to send an email with the same domain as my mailgun account.
Since I had a free mailgun account. I had to change my sender address to my free mailgun address, which was postmaster#sandbox"some long string".mailgun.org
If using nodemailer, you can leave off the sender email or hard code it in.
If using mailgun-js, you have to hard code it in.
My old code:
// setup email data with unicode symbols
let mailOptions = {
from: req.body.from, // sender address
to: 'cu0ngpitt#gmail.com', // list of receivers
subject: 'Someone wrote you from your Online Resume!', // Subject line
text: req.body.messge, // plain text body
};
Corrected code:
// setup email data with unicode symbols
let mailOptions = {
postmaster#sandbox"some long string".mailgun.org, // sender address
to: 'cu0ngpitt#gmail.com', // list of receivers
subject: 'Someone wrote you from your Online Resume!', // Subject line
text: req.body.messge, // plain text body
};