How to send email from Cloudflare Workers, Deno, and Bun (Nodemailer won't)

#webdev #javascript #typescript #opensource

If you've tried sending email from a Cloudflare Worker, a Deno app, or a Bun server, you've probably hit the same wall I did: Nodemailer doesn't run there.

Nodemailer has been the default for ~15 years, and it's excellent — but it's built on Node's net/tls/stream built-ins. On the edge and on non-Node runtimes, those simply don't exist. You end up reaching for a provider's proprietary SDK per environment, or giving up on a unified API.

So I built sently — a runtime-agnostic email library that runs anywhere JavaScript runs.

Nodemailer vs sently

	Nodemailer	sently
Runtimes	Node only	Node, Bun, Deno, CF Workers
Module format	CommonJS	ESM only
Bundle size	~58 KB always	~6 KB HTTP · ~15 KB SMTP
HTTP transports	via plugins	6 built-in
React Email	via plugin	built-in
Idempotency	✗	✓
Webhook parsing	✗	✓
TypeScript	via @types	built-in

The idea

One API, every runtime. sently uses only Web APIs (fetch, Web Crypto, Streams) in its core, so the same code sends mail on Node, Bun, Deno, and Cloudflare Workers. No Node built-ins in the hot path.

Sending via an HTTP provider

Most edge use cases use an HTTP API like Resend or SendGrid. Here's the whole thing:

import { createMailer } from "sently/mailer";
import { ResendTransport } from "sently/transports/resend";

const mailer = await createMailer({
  transport: new ResendTransport({ apiKey: env.RESEND_API_KEY }),
});

await mailer.send({
  from: "you@yourdomain.com",
  to: "user@example.com",
  subject: "Hello from the edge",
  html: "<p>Sent from a Worker.</p>",
});

That exact code runs unmodified in a Cloudflare Worker, a Deno deploy, a Bun server, or plain Node. You only change the transport if you want a different provider.

Why it stays small

sently ships as subpath exports, so you only bundle what you import. A complete HTTP send path (mailer + Resend) is about 6 KB gzip.

For comparison, Nodemailer is ~58 KB min+gzip (measured on Bundlephobia) — and Node-only. So on top of running where Nodemailer can't, the HTTP path is roughly 10× smaller.

SMTP, DKIM, webhooks, idempotency, React Email rendering — all opt-in, none pulled in unless you import them.

Need SMTP instead?

HTTP providers are the common edge case, but classic SMTP relays work too — with pooling, STARTTLS, and DKIM:

import { createSMTPMailer } from "sently";

const mailer = await createSMTPMailer({
  host: "smtp.example.com",
  port: 587,
  auth: { user: "you@example.com", pass: process.env.SMTP_PASS },
});

await mailer.send({
  from: "you@example.com",
  to: "user@example.com",
  subject: "Hello",
  html: "<p>Sent over SMTP.</p>",
});

(SMTP needs raw sockets, so it runs on Node, Bun, and Deno — not inside a Worker, which has no socket access. The HTTP transports above are the edge path.)

A nice local-dev touch

In development you can write emails to disk instead of sending them — no test inbox needed:

import { createMailer } from "sently/mailer";
import { PreviewTransport } from "sently/transports/preview";

const mailer = await createMailer({
  transport: new PreviewTransport({ outDir: ".emails", open: true }),
});

What's in it

HTTP transports: Resend, SendGrid, Postmark, Mailgun, AWS SES, Brevo
SMTP: STARTTLS/TLS, pooling, DKIM (RSA + Ed25519), OAuth2 (Gmail + Microsoft 365)
React Email rendering
Idempotency — dedupe on retry/replay (handy for billing/notification emails)
Bulk send with native provider batch endpoints
Webhook parsing for all six providers, with constant-time signature verification
ESM-native, tree-shakeable, TypeScript-first

Try it

bun add sently   # npm / pnpm / deno / jsr too

It's pre-1.0 but stable — pin an exact version for production. I built it for my own projects and opened it up; feedback and issues are very welcome.

🔗 github.com/alialnaghmoush/sently

What are you using to send email from the edge right now? Curious whether others have hit the same Nodemailer wall — let me know in the comments.