A lightweight SMTP server that forwards emails to a Cloudflare Worker, enabling email sending using 100% Cloudflare infrastructure - no external SMTP providers required.

┌─────────────┐      SMTP       ┌──────────────┐      HTTPS      ┌─────────────────┐
│  Your App   │ ──────────────► │ SMTP Bridge  │ ──────────────► │ Cloudflare      │
│  (n8n, etc) │   Port 2525     │  (Node.js)   │    Webhook      │ Email Worker    │
└─────────────┘                 └──────────────┘                 └────────┬────────┘
                                       │                                  │
                                       ▼                                  ▼
                              ┌─────────────────┐                ┌─────────────────┐
                              │  Health Check   │                │ Email Recipient │
                              │  :2526/health   │                └─────────────────┘
                              └─────────────────┘

• 100% Cloudflare - No external email providers needed
• Free - Uses Cloudflare's free tier (200 emails/day)
• Rate Limiting - Built-in protection against quota exhaustion
• Queue & Retries - SQLite-backed queue with automatic retries
• Multiple Recipients - Full TO/CC/BCC support
• Attachments - Base64-encoded file attachments
• Health Checks - HTTP endpoints for monitoring
• Docker-friendly - Works with containerized applications

First, deploy the email worker to Cloudflare:

cd cloudflare-worker
cp wrangler.toml.example wrangler.toml
# Edit wrangler.toml with your account_id and domain
npm install
wrangler deploy

Set the API key secret:

openssl rand -hex 32  # Generate a key
wrangler secret put API_KEY  # Paste the generated key

# Copy example config
cp .env.example .env

# Edit with your values
nano .env

Required configuration:

WEBHOOK_URL=https://your-worker.workers.dev
WEBHOOK_API_KEY=your-generated-api-key
SMTP_HOST=0.0.0.0
SMTP_PORT=2525

# Install dependencies
npm install

# Run directly
npm start

# Or install as systemd service
sudo ./scripts/install.sh

Point your application's SMTP settings to the bridge:

The bridge includes a built-in rate limiter (default: 200/day) to prevent exceeding Cloudflare's free tier. Adjust RATE_LIMIT_PER_DAY if you have a paid plan.

The bridge exposes HTTP endpoints for monitoring on port 2526 (configurable):

curl http://localhost:2526/health

{
  "status": "healthy",
  "timestamp": "2024-11-26T10:30:00.000Z",
  "uptime": 3600,
  "smtp": {
    "host": "0.0.0.0",
    "port": 2525
  },
  "rateLimit": {
    "used": 45,
    "limit": 200,
    "remaining": 155,
    "resetAt": "2024-11-27T00:00:00.000Z"
  },
  "queue": {
    "enabled": true,
    "total": 50,
    "pending": 2,
    "sent": 45,
    "failed": 3
  }
}

When ENABLE_QUEUE=true (default), emails are:

1. Immediately accepted by SMTP
2. Stored in SQLite database
3. Processed in background
4. Automatically retried on failure

Benefits:

• Fast SMTP responses (no blocking)
• Resilience to Worker downtime
• Automatic retries for transient failures
• Persistent queue survives restarts

To disable: ENABLE_QUEUE=false

Note: Requires better-sqlite3 (optional dependency). Without it, emails are sent immediately without queue/retry.

The bridge supports file attachments:

// Nodemailer example with attachment
await transporter.sendMail({
  from: 'app@yourdomain.com',
  to: 'user@example.com',
  subject: 'Report',
  text: 'Please find attached.',
  attachments: [{
    filename: 'report.pdf',
    path: './report.pdf'
  }]
});

Limitations:

• Max size: 25 MB total (Cloudflare limit)
• Attachments are base64 encoded (33% size increase)
• Large attachments count against rate limits

All recipient types are supported:

await transporter.sendMail({
  from: 'app@yourdomain.com',
  to: ['user1@example.com', 'user2@example.com'],
  cc: 'manager@example.com',
  bcc: 'archive@example.com',
  subject: 'Team Update',
  text: 'Hello team!'
});

Note: Due to Cloudflare Email Routing limitations, each recipient receives an individual email. For 3 TO + 1 CC + 1 BCC, this counts as 5 emails against your daily limit.

smtp-to-webhook/
├── server.js                 # SMTP bridge server
├── package.json
├── .env.example              # Configuration template
├── email_queue.db            # SQLite queue (auto-created)
│
├── cloudflare-worker/        # Cloudflare Worker
│   ├── worker.js             # Worker code
│   ├── wrangler.toml.example # Wrangler config template
│   └── package.json
│
├── scripts/
│   ├── install.sh            # Systemd service installer
│   ├── setup-cloudflare.sh   # Cloudflare Worker setup
│   └── test-smtp.js          # Test script
│
└── docs/
    ├── CLOUDFLARE_SETUP.md   # Detailed Cloudflare setup
    └── integrations/         # App integration guides
        ├── N8N.md
        ├── WORDPRESS.md
        ├── LARAVEL.md
        ├── DJANGO.md
        ├── NEXTCLOUD.md
        └── GITLAB.md

POST https://your-worker.workers.dev
Content-Type: application/json
X-API-Key: your-api-key

{
  "to": ["recipient@example.com"],
  "cc": ["copy@example.com"],
  "bcc": ["blind@example.com"],
  "subject": "Email subject",
  "text": "Plain text body",
  "html": "<p>HTML body</p>",
  "from_name": "Sender Name",
  "attachments": [{
    "filename": "file.pdf",
    "contentType": "application/pdf",
    "content": "base64-encoded-content"
  }],
  "headers": {
    "replyTo": "reply@example.com"
  }
}

Response:

{
  "success": true,
  "message": "Email sent to 3 recipient(s)",
  "recipients": [
    { "email": "recipient@example.com", "type": "to", "status": "sent" },
    { "email": "copy@example.com", "type": "cc", "status": "sent" },
    { "email": "blind@example.com", "type": "bcc", "status": "sent" }
  ],
  "subject": "Email subject"
}

services:
  n8n:
    environment:
      - N8N_EMAIL_MODE=smtp
      - N8N_SMTP_HOST=host.docker.internal
      - N8N_SMTP_PORT=2525
      - N8N_SMTP_SSL=false
      - N8N_SMTP_SENDER=noreply@yourdomain.com
    extra_hosts:
      - "host.docker.internal:host-gateway"

const nodemailer = require('nodemailer');

const transporter = nodemailer.createTransport({
  host: '127.0.0.1',
  port: 2525,
  secure: false
});

await transporter.sendMail({
  from: 'app@yourdomain.com',
  to: 'user@example.com',
  subject: 'Hello',
  text: 'Hello World!',
  attachments: [{
    filename: 'report.pdf',
    path: './report.pdf'
  }]
});

import smtplib
from email.message import EmailMessage

msg = EmailMessage()
msg['From'] = 'app@yourdomain.com'
msg['To'] = 'user@example.com'
msg['Cc'] = 'manager@example.com'
msg['Subject'] = 'Hello'
msg.set_content('Hello World!')

with smtplib.SMTP('127.0.0.1', 2525) as server:
    server.send_message(msg)

# Test the SMTP bridge
npm test your-email@example.com

# Check health status
curl http://localhost:2526/health

# Check rate limit status
curl http://localhost:2526/stats

Error: Rate limit exceeded. Resets at 2024-11-27T00:00:00.000Z

• Check current usage: curl http://localhost:2526/stats
• Wait for reset at midnight UTC
• Or upgrade Cloudflare plan and increase RATE_LIMIT_PER_DAY

• Ensure the bridge is running: systemctl status smtp-bridge
• Check host binding (use 0.0.0.0 for Docker)
• Verify port: nc -zv localhost 2525

• Install optional dependency: npm install better-sqlite3
• Check if queue is enabled: curl http://localhost:2526/health
• View pending emails in email_queue.db

• Verify SPF record exists for your domain
• Add DMARC record: v=DMARC1; p=quarantine
• Use consistent sender address

• The SMTP bridge has no authentication by default
• Only bind to 127.0.0.1 unless Docker requires 0.0.0.0
• Use firewall rules to restrict access to ports 2525 and 2526
• Keep API keys secure and rotate regularly

1. 200 emails/day on free tier - Each recipient counts separately
2. No DKIM signing - Cloudflare Email Routing handles authentication
3. No email tracking - Opens/clicks not tracked
4. Sequential recipient delivery - CC/BCC recipients get individual emails
5. 25 MB max email size - Including base64-encoded attachments

• Node.js 18+
• npm
• Domain with Cloudflare DNS
• Cloudflare Email Routing enabled
• (Optional) better-sqlite3 for queue functionality

MIT

Built with:

• smtp-server - SMTP server
• mailparser - Email parsing
• better-sqlite3 - Queue storage
• Cloudflare Workers - Serverless execution
• Cloudflare Email Routing - Email infrastructure