SMTP relay that just delivers

// PHPMailer over SMTP
use PHPMailer\PHPMailer\PHPMailer;

$mail = new PHPMailer(true);
$mail->isSMTP();
$mail->Host       = 'smtp.sendorx.com';
$mail->Port       = 587;
$mail->SMTPAuth   = true;
$mail->Username   = 'info@sendorx.com';
$mail->Password   = getenv('SENDORX_SMTP_KEY');
$mail->SMTPSecure = PHPMailer::ENCRYPTION_STARTTLS;

$mail->setFrom('sender@yourdomain.com', 'Your App');
$mail->addAddress('recipient@example.com');
$mail->Subject = 'Hello from SendorX';
$mail->Body    = 'It works!';
$mail->send();

import os, smtplib
from email.message import EmailMessage

msg = EmailMessage()
msg['From']    = 'sender@yourdomain.com'
msg['To']      = 'recipient@example.com'
msg['Subject'] = 'Hello from SendorX'
msg.set_content('It works!')

with smtplib.SMTP('smtp.sendorx.com', 587) as s:
    s.starttls()
    s.login('info@sendorx.com', os.environ['SENDORX_SMTP_KEY'])
    s.send_message(msg)

// nodemailer over SMTP
const nodemailer = require('nodemailer');

const transport = nodemailer.createTransport({
  host: 'smtp.sendorx.com',
  port: 587,
  secure: false,
  auth: {
    user: 'info@sendorx.com',
    pass: process.env.SENDORX_SMTP_KEY
  }
});

await transport.sendMail({
  from: '"Your App" <sender@yourdomain.com>',
  to:   'recipient@example.com',
  subject: 'Hello from SendorX',
  text:    'It works!'
});