Receive email in real time with Node.js / TypeScript

Receive email in Node.js / TypeScript with a signed JSON webhook: install the SDK, run a receiver, configure a MailKite address, and test delivery. Here, live means event-driven delivery after the email arrives, with normal SMTP and forwarding delays; it does not promise an exact latency.

1. Prepare a receiving address

In MailKite, add a domain or claim an available hosted subdomain. Complete the verification shown in the dashboard before receiving. For your own domain, publish the exact MX record MailKite returns. Choose an address such as inbound@your-receiving-domain.

For a detailed setup walkthrough, use the quickstart and domain verification docs. Your HTTP receiver needs a public HTTPS URL; a development tunnel can expose local port 3000 during testing.

The shared demo repository contains the exact receiver sources, local checks and inbox inspector used by this series.

2. Configure the webhook and run the Node.js / TypeScript receiver

Create a webhook route matching your receiving address and point it to https://your-app.example/hooks/mailkite, replacing the example host with your public HTTPS host. Copy that route's signing secret into the receiver's environment. Avoid a catch-all route if you only want mail for one address.

Node.js 22.13+ for the built-in node:sqlite module used here. Set MAILKITE_WEBHOOK_SECRET to the signing secret for your configured MailKite webhook, supplied through your environment or secret manager. You do not need an API key for local signature verification.

npm init -y
npm install mailkite express

Mount express.raw() on this route before any global express.json() middleware. The SDK accepts the original Buffer. The example uses synchronous SQLite inserts as a small local inbox. TypeScript apps can use the same SDK and endpoint; preserve the Buffer rather than assuming req.body is a parsed object.

// Docs: docs/website/content/live-receiving-email-series.md
import express from "express";
import { DatabaseSync } from "node:sqlite";
import { MailKite } from "mailkite";

const secret = process.env.MAILKITE_WEBHOOK_SECRET;
if (!secret) throw new Error("Set MAILKITE_WEBHOOK_SECRET");
const db = new DatabaseSync(process.env.INBOX_DB || "inbox.sqlite");
db.exec("PRAGMA busy_timeout = 5000");
db.exec("CREATE TABLE IF NOT EXISTS inbox (id TEXT PRIMARY KEY, payload TEXT NOT NULL)");
const insert = db.prepare("INSERT INTO inbox (id, payload) VALUES (?, ?) ON CONFLICT(id) DO NOTHING");
const app = express();
app.post("/hooks/mailkite", express.raw({ type: "application/json", limit: "10mb" }), (req, res) => {
  if (!Buffer.isBuffer(req.body) || !MailKite.verifyWebhook(req.get("x-mailkite-signature") || "", req.body, secret)) {
    return res.sendStatus(401);
  }
  let event;
  try { event = JSON.parse(req.body.toString("utf8")); }
  catch { return res.sendStatus(400); }
  if (!event || typeof event !== "object" || Array.isArray(event)) return res.sendStatus(400);
  if (event.type === "email.received") {
    if (typeof event.id !== "string" || !event.id) return res.sendStatus(400);
    try { insert.run(event.id, req.body.toString("utf8")); }
    catch { return res.sendStatus(503); }
  }
  return res.json({ status: "ok" });
});
app.listen(Number(process.env.PORT || 3000));

Download the exact receiver shown above. Save it beside its dependencies, then start it with the environment variable already set:

node receive.mjs

This example stores each event once in a local SQLite inbox before returning success. Use persistent disk; an ephemeral deployment can delete that inbox on restart. A separate worker should process stored events and track completion. Storage deduplication alone does not make external side effects exactly-once.

3. Test the exact receiver and address

Download the local signed test and run it with Node.js and the same webhook secret. It creates synthetic HTTP requests only, including a duplicate id and a tampered body; it sends no email. The first two requests should return the SDK's JSON acknowledgement, and the tampered one should return 401.

node check.mjs http://127.0.0.1:3000/hooks/mailkite

Then send a real message to the exact receiving address to test routing. The dashboard's domain-webhook test uses a catch-all route; it does not test an exact-address route. See signature verification and delivery and retries.

Download the local inbox inspector to read stored message bodies, including Gmail's confirmation message. This displays mailbox contents in your own terminal; keep it off the public web.

python3 inspect-inbox.py inbox.sqlite

4. Check a real message and its payload

Send a new message to the MailKite receiving address. Confirm delivery in MailKite and receipt at the endpoint. The JSON event has type: "email.received", a stable id, sender and recipient address objects, decoded bodies, attachment metadata and authentication results.

• Body: use text, falling back to textFromHtml when the plain-text part is null.
• Attachments: process the signed download URLs after durable acceptance, before they expire.
• Authentication: the webhook signature authenticates MailKite's delivery. It does not prove the original sender is trustworthy. Forwarding can change email-authentication results.
• Retries: replay a delivery and confirm your production handler does not create a second job for the same message id.

Troubleshoot the delivery boundary

Continue with the complete event reference, other receiving guides or the companion implementation article.