SMTP2Webhook

A lightweight Rust application that runs an SMTP server and forwards incoming emails to a configurable HTTP webhook.

Bridges the gap for software that only supports email notifications (monitoring tools, alerting systems) to modern webhook-based services like Discord, Slack, or any HTTP endpoint.

Features

• 🚀 Lightweight SMTP server
• 🔗 Forwards emails to HTTP webhooks as JSON
• 🔄 Automatic retry logic with exponential backoff
• ⚙️ Simple TOML configuration
• 🔓 Accepts any SMTP authentication (designed for local/internal use)
• 📝 Structured logging

Quick Start

Using Docker (Recommended)

# Pull image from GitHub Container Registry
docker pull ghcr.io/seanmarpo/smtp2webhook:latest

# Create config file
cp config.toml.example config.toml
# Edit config.toml with your webhook URL

# Run with docker-compose
docker-compose up -d

# Or run directly
docker run -d \
  --name smtp2webhook \
  -p 2525:2525 \
  -v $(pwd)/config.toml:/app/config.toml:ro \
  ghcr.io/seanmarpo/smtp2webhook:latest

Building from Source

Prerequisites: Rust 1.80 or higher

# Build
cargo build --release

# Configure
cp config.toml.example config.toml
# Edit config.toml with your webhook URL

# Run
cargo run --release

Configuration

[smtp]
bind_address = "127.0.0.1:2525"  # Use "0.0.0.0:2525" for Docker
hostname = "localhost"

[webhook]
url = "http://localhost:8080/webhook"
max_retries = 3
timeout_secs = 30

# Optional: Custom headers for authentication
[webhook.headers]
Authorization = "Bearer your-token-here"
X-API-Key = "your-api-key"

[logging]
level = "info"  # trace, debug, info, warn, error

Webhook Payload

Emails are sent as JSON POST requests:

{
  "from": "sender@example.com",
  "to": ["recipient@example.com"],
  "subject": "Email Subject",
  "body": "Plain text email body content",
  "attachments": ["document.pdf", "image.png"]
}

Content Handling:

• Plain text emails delivered as-is
• HTML emails automatically converted to plain text
• Multipart emails use plain text version
• Base64 and Quoted-Printable encodings automatically decoded
• Attachment filenames listed (content not included)

Testing

# Run Rust tests
cargo test

# Send test email
./testing/test_send_email.sh

# Test webhook receiver (separate terminal)
./testing/test_webhook.py

# Run all integration tests
./testing/run_all_tests.sh

Docker

Images

Pre-built images are available from GitHub Container Registry:

# Latest release
docker pull ghcr.io/seanmarpo/smtp2webhook:latest

# Specific version
docker pull ghcr.io/seanmarpo/smtp2webhook:v0.1.0

Or build locally:

docker build -t smtp2webhook .

Configuration Notes

• Default port: 2525
• For Docker networking, use bind_address = "0.0.0.0:2525"
• Mount config as read-only: -v $(pwd)/config.toml:/app/config.toml:ro
• Use service names in docker-compose: http://service-name:port/webhook

Error Handling

• Failed webhook requests retry up to max_retries times with exponential backoff
• After exhausting retries, email is dropped and error logged
• SMTP server responds with success to prevent email bounces

Security Warning

⚠️ For local/internal use only!

• Accepts any SMTP authentication
• No TLS/SSL support
• Do not expose to public internet
• Use Docker networks to isolate containers

License

See LICENSE file for details.