Send email over SMTP

Send transactional emails over Cloudflare Email Service authenticated SMTP (smtp.mx.cloudflare.net:465) from any SMTP-capable language or client.

Prerequisites

A domain onboarded for Email Sending.
A Cloudflare API token with the Email Sending: Edit permission. Set it as CF_API_TOKEN in your environment. The token is used as the SMTP password; the username is the literal string api_token.

Send an email

cat > mail.txt <<EOF
From: welcome@yourdomain.com
To: recipient@example.com
Subject: Welcome to our service!

Thanks for signing up.
EOF

curl --ssl-reqd \
  --url "smtps://smtp.mx.cloudflare.net:465" \
  --user "api_token:$CF_API_TOKEN" \
  --mail-from "welcome@yourdomain.com" \
  --mail-rcpt "recipient@example.com" \
  --upload-file mail.txt

The sender domain must be onboarded for Email Sending on the account that owns the API token.

Install Nodemailer ↗ with npm install nodemailer.

Send an email

import nodemailer from "nodemailer";

const transporter = nodemailer.createTransport({
	host: "smtp.mx.cloudflare.net",
	port: 465,
	secure: true, // implicit TLS
	auth: {
		user: "api_token",
		pass: process.env.CF_API_TOKEN,
	},
});

const info = await transporter.sendMail({
	from: '"Acme" <welcome@yourdomain.com>',
	to: "user@example.com",
	subject: "Welcome to Acme",
	text: "Thanks for signing up.",
	html: "<h1>Welcome to Acme</h1><p>Thanks for signing up.</p>",
});

console.log("Message sent:", info.messageId);

Send with an attachment

const info = await transporter.sendMail({
	from: '"Acme Billing" <billing@yourdomain.com>',
	to: "customer@example.com",
	subject: "Your invoice",
	text: "Please find your invoice attached.",
	attachments: [
		{
			filename: "invoice-2026-04.pdf",
			path: "./invoices/invoice-2026-04.pdf",
			contentType: "application/pdf",
		},
	],
});

Total message size (including base64-encoded attachments) must not exceed 5 MiB. See Limits.

Error handling

Nodemailer rejects the promise with an Error whose .responseCode reflects the SMTP reply code. See SMTP response codes and Troubleshooting.

try {
	await transporter.sendMail({
		/* ... */
	});
} catch (err) {
	console.error(err.responseCode, err.message);
}

Uses the standard-library smtplib ↗ (Python 3.8 or later).

Send an email

import os
import smtplib
from email.message import EmailMessage

msg = EmailMessage()
msg["From"] = "Acme <welcome@yourdomain.com>"
msg["To"] = "user@example.com"
msg["Subject"] = "Welcome to Acme"
msg.set_content("Thanks for signing up.")
msg.add_alternative(
    "<h1>Welcome to Acme</h1><p>Thanks for signing up.</p>",
    subtype="html",
)

with smtplib.SMTP_SSL("smtp.mx.cloudflare.net", 465) as s:
    s.login("api_token", os.environ["CF_API_TOKEN"])
    s.send_message(msg)

smtplib.SMTP_SSL opens an implicit-TLS connection on port 465, which is what Cloudflare's SMTP endpoint requires. Do not use smtplib.SMTP with starttls(); STARTTLS is not supported.

Send to multiple recipients

msg["To"] = ", ".join([
    "user1@example.com",
    "user2@example.com",
    "user3@example.com",
])

A single SMTP session can deliver to up to 50 RCPT TO addresses. See Limits.

Send with an attachment

from pathlib import Path

pdf = Path("invoice-2026-04.pdf").read_bytes()
msg.add_attachment(
    pdf,
    maintype="application",
    subtype="pdf",
    filename="invoice-2026-04.pdf",
)

Error handling

smtplib raises subclasses of smtplib.SMTPException with the SMTP reply code attached. See SMTP response codes and Troubleshooting.

try:
    with smtplib.SMTP_SSL("smtp.mx.cloudflare.net", 465) as s:
        s.login("api_token", os.environ["CF_API_TOKEN"])
        s.send_message(msg)
except smtplib.SMTPAuthenticationError as e:
    print(f"Auth failed: {e.smtp_code} {e.smtp_error!r}")
except smtplib.SMTPResponseException as e:
    print(f"SMTP error: {e.smtp_code} {e.smtp_error!r}")

Send an email

<?php
use PHPMailer\PHPMailer\PHPMailer;

require 'vendor/autoload.php';

$mail = new PHPMailer(true);
$mail->isSMTP();
$mail->Host       = 'smtp.mx.cloudflare.net';
$mail->Port       = 465;
$mail->SMTPSecure = PHPMailer::ENCRYPTION_SMTPS;
$mail->SMTPAuth   = true;
$mail->Username   = 'api_token';
$mail->Password   = getenv('CF_API_TOKEN');

$mail->setFrom('welcome@yourdomain.com', 'Acme');
$mail->addAddress('recipient@example.com');
$mail->Subject = 'Welcome to our service!';
$mail->Body    = 'Thanks for signing up.';
$mail->send();

Next steps

SMTP reference — connection details, authentication, response codes, and troubleshooting.
Specify recipients — multiple recipients, CC and BCC, and named addresses.
Limits — account, message, and session limits.