SMTP relay service for the email your app already sends.

# .env
MAIL_MAILER=smtp
MAIL_HOST=[SMTP host]
MAIL_PORT=[port]
MAIL_USERNAME="[issued at onboarding]"
MAIL_PASSWORD="[issued at onboarding]"
# TLS / encryption: [confirm at onboarding]
MAIL_FROM_ADDRESS="no-reply@yourdomain.com"
MAIL_FROM_NAME="${APP_NAME}"

# settings.py
EMAIL_BACKEND = "django.core.mail.backends.smtp.EmailBackend"
EMAIL_HOST = "[SMTP host]"
EMAIL_PORT = [port]
EMAIL_HOST_USER = os.environ["TINYRELAY_SMTP_USER"]      # issued at onboarding
EMAIL_HOST_PASSWORD = os.environ["TINYRELAY_SMTP_PASS"]  # issued at onboarding
# EMAIL_USE_TLS / EMAIL_USE_SSL: [confirm at onboarding]
DEFAULT_FROM_EMAIL = "no-reply@yourdomain.com"

# config/environments/production.rb
config.action_mailer.delivery_method = :smtp
config.action_mailer.smtp_settings = {
  address:   "[SMTP host]",
  port:      [port],
  user_name: ENV["TINYRELAY_SMTP_USER"], # issued at onboarding
  password:  ENV["TINYRELAY_SMTP_PASS"]  # issued at onboarding
  # authentication / TLS options: [confirm at onboarding]
}

import nodemailer from "nodemailer";

const transporter = nodemailer.createTransport({
  host: "[SMTP host]",
  port: [port],
  // secure / STARTTLS: [confirm at onboarding]
  auth: {
    user: process.env.TINYRELAY_SMTP_USER, // issued at onboarding
    pass: process.env.TINYRELAY_SMTP_PASS,
  },
});

await transporter.sendMail({
  from: '"Acme" <no-reply@acme.com>',
  to: "ann@example.com",
  subject: "Reset your password",
  html: "<p>Use this link to reset your password.</p>",
});

use PHPMailer\PHPMailer\PHPMailer;

$mail = new PHPMailer(true);
$mail->isSMTP();
$mail->Host     = '[SMTP host]';
$mail->Port     = [port];
$mail->SMTPAuth = true;
$mail->Username = getenv('TINYRELAY_SMTP_USER'); // issued at onboarding
$mail->Password = getenv('TINYRELAY_SMTP_PASS');
// $mail->SMTPSecure = [confirm at onboarding];
$mail->setFrom('no-reply@acme.com', 'Acme');
$mail->addAddress('ann@example.com');
$mail->isHTML(true);
$mail->Subject = 'Reset your password';
$mail->Body    = '<p>Use this link to reset your password.</p>';
$mail->send();

# Any SMTP client
Setting        Value
-------------  ------------------------------------------
Host           [SMTP host]
Port           [port]
Encryption     [confirm at onboarding]
Username       issued at onboarding
Password       issued at onboarding
From address   a sender on a domain you shared with us