Direct SMTP delivery from Cloudflare Workers.

@workermailer/smtp keeps SMTP inside the Worker runtime with TCP sockets, DSN support, lifecycle hooks, attachments, and queue helpers.

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Highlights

Built for SMTP on the edge.

Cloudflare TCP sockets with SMTP auth modes.
DSN, hooks, attachments, inline CID assets, and explicit errors.
Queue helpers for async delivery off the request path.

terminal Install with Bun

bun add @workermailer/smtp

send-email.ts Quick start

import { WorkerMailer } from '@workermailer/smtp'

const mailer = await WorkerMailer.connect({
  host: 'smtp.example.com',
  port: 465,
  secure: true,
  authType: 'plain',
  credentials: {
    username: env.SMTP_USERNAME,
    password: env.SMTP_PASSWORD
  }
})

await mailer.send({
  from: { name: 'Worker Mailer', email: 'noreply@example.com' },
  to: { name: 'Alice', email: 'alice@example.com' },
  subject: 'Hello from the edge',
  text: 'This message was sent from a Cloudflare Worker.',
  html: '<h1>Hello from the edge</h1><p>SMTP over TCP sockets.</p>'
})

Queues

Queue helpers for bursty traffic.

Move email processing into Cloudflare Queues when you need retries, backpressure, or batching across requests.

queue.ts Queue handler

import {
  createQueueHandler,
  enqueueEmail,
  type QueueEmailMessage
} from '@workermailer/smtp/queue'

interface Env {
  EMAIL_QUEUE: Queue<QueueEmailMessage>
}

export default {
  async fetch(_request: Request, env: Env) {
    await enqueueEmail(env.EMAIL_QUEUE, {
      mailerOptions: {
        host: 'smtp.example.com',
        port: 465,
        secure: true,
        credentials: {
          username: env.SMTP_USERNAME,
          password: env.SMTP_PASSWORD
        }
      },
      emailOptions: {
        from: 'noreply@example.com',
        to: 'alice@example.com',
        subject: 'Queued email',
        text: 'Sent from Cloudflare Queues.'
      }
    })

    return new Response('queued')
  },

  async queue(batch: MessageBatch<QueueEmailMessage>) {
    const handleQueue = createQueueHandler()
    await handleQueue(batch)
  }
}

Need Resend instead?

Use the Resend library for API-based delivery with the same queue patterns.

View Resend library Read SMTP docs