Free transactional email

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>",
});

POST /v1/send  HTTP/1.1
Host: api.mailkite.dev
Authorization: Bearer mk_live_3a9f…
Content-Type: application/json

{
  "from": "hello@myapp.ai",
  "to": "ada@example.com",
  "subject": "Your invoice #1042",
  "html": "<p>Thanks! Receipt attached.</p>",
  "attachments": [
    { "filename": "receipt.pdf", "url": "https://…" }
  ]
}

← 202 Accepted
{ "id": "msg_2Hk9…", "status": "queued" }

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>"
  }'

import express from "express";
import { MailKite } from "mailkite";

const app = express();
app.use(express.json());

app.post("/hooks/mailkite", (req, res) => {
  // Verify the signature in production — see /docs/webhook-security
  const email = req.body; // { from, subject, text, html, attachments }
  res.json(MailKite.replyOk()); // {"status":"ok"}
});

POST /your/webhook  HTTP/1.1
Content-Type: application/json

{
  "from": "ada@example.com",
  "to": "hello@myapp.ai",
  "subject": "Re: invoice #1042",
  "text": "Looks good — approved!",
  "html": "<p>Looks good — approved!</p>",
  "attachments": [
    {
      "id": "msg_8f3a...:0",
      "filename": "po.pdf",
      "contentType": "application/pdf",
      "size": 18213,
      "url": "https://api.mailkite.dev/att/9f86d0c2"
    }
  ],
  "messageId": "<a1b2c3@mail.example.com>",
  "receivedAt": "2026-06-19T17:42:10Z"
}

from flask import Flask, request
from mailkite import reply_ok

app = Flask(__name__)

@app.post("/hooks/mailkite")
def hook():
    # Verify the signature in production — see /docs/webhook-security
    email = request.get_json()  # { "from", "subject", "text", ... }
    return reply_ok(), 200, {"content-type": "application/json"}

<?php
$mk = new \MailKite\Client("");
// Verify the signature in production — see /docs/webhook-security
$email = json_decode(file_get_contents("php://input"), true);
header("content-type: application/json");
echo $mk->replyOk(); // {"status":"ok"}

// Spring Boot
@PostMapping(value = "/hooks/mailkite", produces = "application/json")
public String mailkite(@RequestBody Map<String, Object> email) {
    MailKite mk = new MailKite("");
    // Verify the signature in production — see /docs/webhook-security
    return mk.replyOk(); // {"status":"ok"}
}

http.HandleFunc("/hooks/mailkite", func(w http.ResponseWriter, r *http.Request) {
	// Verify the signature in production — see /docs/webhook-security
	var email map[string]any
	json.NewDecoder(r.Body).Decode(&email)
	w.Header().Set("content-type", "application/json")
	w.Write([]byte(mailkite.ReplyOk())) // {"status":"ok"}
})

require "sinatra"
require "json"
require "mailkite"

post "/hooks/mailkite" do
  # Verify the signature in production — see /docs/webhook-security
  email = JSON.parse(request.body.read)
  content_type :json
  Mailkite.reply_ok # {"status":"ok"}
end