Send email with Cloudflare
Transactional email is the mail your app sends one recipient at a time — receipts, password resets, magic links, notifications. This guide sends one through Cloudflare Email Service — from a Worker, the REST API, or SMTP — then shows the same send on MailKite.
What you'll need
- A domain in your Cloudflare account, with access to its DNS.
- A Worker project (Wrangler); for the REST API or SMTP, a Cloudflare API token with email sending permission.
Email Sending is the transactional half of Cloudflare Email Service. At the time of writing it is in beta on the Workers Paid plan; check the Email Service docs for current availability and limits.
Part 1 — Send with Cloudflare
1. Onboard your sending domain
In the dashboard, go to Compute & AI → Email Service → Email Sending
and select Onboard Domain. Because the domain is already on Cloudflare,
it writes the authentication records for you — an SPF include, a DKIM key on the
cf-bounce selector, a DMARC policy, and an MX record that routes
bounces back to Cloudflare:
Type Name Value
TXT yourdomain.com v=spf1 include:_spf.mx.cloudflare.net ~all
TXT cf-bounce._domainkey.yourdomain.com (DKIM key — written for you on onboard)
TXT _dmarc.yourdomain.com v=DMARC1; p=none;
MX cf-bounce.yourdomain.com (bounce route — written for you on onboard)
The same setup is available from the CLI with
npx wrangler email sending enable yourdomain.com. DNS usually
propagates within a few minutes.
2. Send from a Worker
Declare a send binding in your Wrangler config. It needs no API key — the binding is the credential:
// wrangler.jsonc
{
"send_email": [
{ "name": "EMAIL" }
]
}
Then call env.EMAIL.send() inside your handler with a structured
message. The current binding takes to/from/
subject/html/text directly — no MIME to
assemble. The from address must be on the domain you onboarded:
export default {
async fetch(request, env) {
const res = await env.EMAIL.send({
to: "ada@example.com",
from: "hello@yourdomain.com",
subject: "Your invoice #1042",
html: "<p>Thanks! Your receipt is attached.</p>",
text: "Thanks! Your receipt is attached.",
});
return new Response(`Sent: ${res.messageId}`);
},
};
A raw-MIME path also exists — EmailMessage from
cloudflare:email built with the mimetext library — but
the structured send() above is the current, simpler form.
3. Or send over the REST API
From outside Workers, POST to the Email Sending endpoint with an
API token. The body is the same flat shape as the binding:
curl -X POST \
"https://api.cloudflare.com/client/v4/accounts/$CF_ACCOUNT_ID/email/sending/send" \
-H "Authorization: Bearer $CF_API_TOKEN" \
-H "Content-Type: application/json" \
-d '{
"to": "ada@example.com",
"from": "hello@yourdomain.com",
"subject": "Your invoice #1042",
"html": "<p>Thanks! Your receipt is attached.</p>",
"text": "Thanks! Your receipt is attached."
}' ← 200 OK
{ "success": true,
"result": { "delivered": ["ada@example.com"], "queued": [], "permanent_bounces": [] } } 4. Or send over SMTP
Cloudflare also exposes an SMTP relay. The username is the literal
api_token and the password is your API token:
Host: smtp.mx.cloudflare.net
Port: 465 # SMTPS (implicit TLS)
Username: api_token
Password: <your Cloudflare API token>
From: hello@yourdomain.com That's a transactional send on Cloudflare: onboard the domain, then call the Worker binding, the REST API, or the SMTP relay.
Part 2 — The same, on MailKite
MailKite sends from any runtime over a plain HTTP POST or SMTP —
no Worker to deploy, no MIME to assemble — and the same verified domain also
receives. When we built sending into MailKite, we wanted three things to be
true: one set of DNS records, one API key that works for both HTTP and SMTP,
and a body you don't have to nest. Here's the same message.
1. Authenticate your domain
Publish three TXT records — SPF, a MailKite DKIM key, and DMARC.
The same domain also receives mail once its MX points at MailKite:
Type Name Value
TXT yourdomain.com v=spf1 include:mailkite.dev ~all
TXT mailkite._domainkey.yourdomain.com v=DKIM1; k=rsa; p=…
TXT _dmarc.yourdomain.com v=DMARC1; p=none; The exact DKIM value is shown in the dashboard; MailKite verifies the records for you over DNS.
2. Send over the API
One POST /v1/send with a flat from/to/
subject/html body. A 202 means it's
queued:
Pick your language in the card — the dashboard and the AI assistant do the same send, and every SDK takes the same fields:
Messages → Compose
From hello@myapp.ai
To ada@example.com
Subject Your invoice #1042
Body Thanks! Receipt attached.
Click [ Send ]Email ada@example.com from hello@myapp.ai
with subject "Your invoice #1042" and body "Thanks! Receipt attached."import { MailKite } from "mailkite";
const mk = new MailKite(process.env.MAILKITE_API_KEY);
const { id, status } = await mk.send({
from: "hello@myapp.ai",
to: "ada@example.com",
subject: "Your invoice #1042",
html: "<p>Thanks! Receipt attached.</p>",
});import os
from mailkite import MailKite
mk = MailKite(os.environ["MAILKITE_API_KEY"])
res = mk.send({
"from": "hello@myapp.ai",
"to": "ada@example.com",
"subject": "Your invoice #1042",
"html": "<p>Thanks! Receipt attached.</p>",
})<?php
$mk = new \MailKite\Client(getenv('MAILKITE_API_KEY'));
$res = $mk->send([
'from' => 'hello@myapp.ai',
'to' => 'ada@example.com',
'subject' => 'Your invoice #1042',
'html' => '<p>Thanks! Receipt attached.</p>',
]);MailKite mk = new MailKite(System.getenv("MAILKITE_API_KEY"));
Object res = mk.send(Map.of(
"from", "hello@myapp.ai",
"to", "ada@example.com",
"subject", "Your invoice #1042",
"html", "<p>Thanks! Receipt attached.</p>"
));mk := mailkite.New(os.Getenv("MAILKITE_API_KEY"))
res, err := mk.Send(mailkite.Message{
From: "hello@myapp.ai",
To: "ada@example.com",
Subject: "Your invoice #1042",
HTML: "<p>Thanks! Receipt attached.</p>",
})require "mailkite"
mk = Mailkite::Client.new(ENV["MAILKITE_API_KEY"])
res = mk.send(
"from" => "hello@myapp.ai",
"to" => "ada@example.com",
"subject" => "Your invoice #1042",
"html" => "<p>Thanks! Receipt attached.</p>"
)curl https://api.mailkite.dev/v1/send \
-H "Authorization: Bearer $MAILKITE_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"from": "hello@myapp.ai",
"to": "ada@example.com",
"subject": "Your invoice #1042",
"html": "<p>Thanks! Receipt attached.</p>"
}' Messages → Sent
● queued msg_2Hk9… ada@example.com Your invoice #1042Sent — message msg_2Hk9…, status queued.← 202 Accepted
{ "id": "msg_2Hk9…", "status": "queued" }← 202 Accepted
{ "id": "msg_2Hk9…", "status": "queued" }← 202 Accepted
{ "id": "msg_2Hk9…", "status": "queued" }← 202 Accepted
{ "id": "msg_2Hk9…", "status": "queued" }← 202 Accepted
{ "id": "msg_2Hk9…", "status": "queued" }← 202 Accepted
{ "id": "msg_2Hk9…", "status": "queued" }← 202 Accepted
{ "id": "msg_2Hk9…", "status": "queued" } 3. Or send over SMTP
The same key is your SMTP password — no separate credential to generate:
import nodemailer from "nodemailer";
const tx = nodemailer.createTransport({
host: "smtp.mailkite.dev",
port: 587, // STARTTLS · use 465 for implicit TLS
auth: {
user: "mailkite", // any username works
pass: process.env.MAILKITE_API_KEY, // your mk_live_… key
},
});
await tx.sendMail({
from: "hello@myapp.ai", // an address on a verified domain
to: "ada@example.com",
subject: "Your invoice #1042",
html: "<p>Thanks! Receipt attached.</p>",
});import os, smtplib
from email.message import EmailMessage
msg = EmailMessage()
msg["From"] = "hello@myapp.ai" # an address on a verified domain
msg["To"] = "ada@example.com"
msg["Subject"] = "Your invoice #1042"
msg.set_content("Thanks! Receipt attached.")
# Standard library — no dependency to install.
with smtplib.SMTP("smtp.mailkite.dev", 587) as s:
s.starttls()
s.login("mailkite", os.environ["MAILKITE_API_KEY"]) # password = your key
s.send_message(msg)<?php
use PHPMailer\PHPMailer\PHPMailer;
$mail = new PHPMailer(true);
$mail->isSMTP();
$mail->Host = 'smtp.mailkite.dev';
$mail->SMTPAuth = true;
$mail->Username = 'mailkite'; // any username
$mail->Password = getenv('MAILKITE_API_KEY'); // your mk_live_… key
$mail->SMTPSecure = PHPMailer::ENCRYPTION_STARTTLS;
$mail->Port = 587; // or 465 for implicit TLS
$mail->setFrom('hello@myapp.ai'); // an address on a verified domain
$mail->addAddress('ada@example.com');
$mail->Subject = 'Your invoice #1042';
$mail->Body = 'Thanks! Receipt attached.';
$mail->send();Properties p = new Properties();
p.put("mail.smtp.host", "smtp.mailkite.dev");
p.put("mail.smtp.port", "587"); // 465 for implicit TLS
p.put("mail.smtp.auth", "true");
p.put("mail.smtp.starttls.enable", "true");
Session s = Session.getInstance(p, new Authenticator() {
protected PasswordAuthentication getPasswordAuthentication() {
// username = anything · password = your mk_live_… key
return new PasswordAuthentication("mailkite", System.getenv("MAILKITE_API_KEY"));
}
});
Message msg = new MimeMessage(s);
msg.setFrom(new InternetAddress("hello@myapp.ai")); // a verified domain
msg.setRecipients(Message.RecipientType.TO, InternetAddress.parse("ada@example.com"));
msg.setSubject("Your invoice #1042");
msg.setText("Thanks! Receipt attached.");
Transport.send(msg);auth := smtp.PlainAuth("", "mailkite", os.Getenv("MAILKITE_API_KEY"), "smtp.mailkite.dev")
msg := []byte("From: hello@myapp.ai\r\n" + // an address on a verified domain
"To: ada@example.com\r\n" +
"Subject: Your invoice #1042\r\n\r\n" +
"Thanks! Receipt attached.\r\n")
// STARTTLS on 587; SendMail upgrades the connection before AUTH.
err := smtp.SendMail("smtp.mailkite.dev:587", auth,
"hello@myapp.ai", []string{"ada@example.com"}, msg)require "mail"
Mail.defaults do
delivery_method :smtp, {
address: "smtp.mailkite.dev",
port: 587, # 465 for implicit TLS
user_name: "mailkite", # any username
password: ENV["MAILKITE_API_KEY"], # your mk_live_… key
enable_starttls_auto: true,
}
end
Mail.deliver do
from "hello@myapp.ai" # an address on a verified domain
to "ada@example.com"
subject "Your invoice #1042"
body "Thanks! Receipt attached."
end See Send API and SMTP relay for the full reference — attachments, headers, and delivery events.
A little about MailKite
MailKite is programmable email for developers and AI agents. One API key and
one set of DNS records cover both directions: send with a single
POST (or the SMTP relay), and the same verified domain receives
replies as a signed webhook of clean JSON.
Behind the send, MailKite routes across multiple providers to keep you in the
inbox — and any address can be handed to an agent
that reads and replies on its own. Sending and receiving are on the
free tier.
Next: the Send API for attachments and delivery tracking, or the Quickstart to get a verified domain and API key.