SMTP Relay Server

A lightweight SMTP relay server written in Go, designed for efficient email delivery with configurable rate limiting and TLS support.

Features

• Supports multiple SMTP protocols:
  • SMTPS/TLS (port 465)
  • STARTTLS (port 587)
  • Unencrypted SMTP (port 25)
• Configurable encryption per listener
• Configurable rate limiting
• IP blocking
• Multi-platform support (Windows, Linux, MacOS)
• Detailed logging
• Automatic service installation
• Comprehensive service management
• Log rotation and monitoring

Installation

Prerequisites

• Go 1.20+ installed
• Git installed
• System administrator privileges

Quick Start

1. Clone the repository:

git clone https://github.com/WikiHacker/go-relay-server.git
cd go-relay-server

2. Install dependencies:

go mod download

3. Configure the server by editing config/config.json

4. Compile the server:

# Linux/MacOS
chmod +x script/compile.sh
./script/compile.sh

# Windows
./script/compile.ps1

5. Install and start the service:

# Linux/MacOS
sudo ./script/setup-installation.sh

# Windows (Run as Administrator)
.\script\setup-installation.ps1

Configuration

Edit config/config.json with your desired settings:

{
  "Listeners": [
    {
      "host": "0.0.0.0",
      "port": "25",
      "encryption": "none",
      "require_auth": false
    },
    {
      "host": "0.0.0.0", 
      "port": "465",
      "encryption": "tls",
      "require_auth": true
    },
    {
      "host": "0.0.0.0",
      "port": "587",
      "encryption": "starttls",
      "require_auth": true
    }
  ],
  "DefaultRelay": "smtp.example.com:25",
  "TLSCertFile": "certs/cert.pem",
  "TLSKeyFile": "certs/key.pem",
  "RateLimiting": {
    "RequestsPerMinute": 100,
    "BurstLimit": 20,
    "ExemptIPs": ["127.0.0.1"]
  },
  "BlockList": ["spamdomain.com"]
}

Service Management

The server provides comprehensive service management through the manage-service.sh script:

Installation

sudo ./script/manage-service.sh install [install-dir]

Common Operations

• Start service: sudo ./script/manage-service.sh start
• Stop service: sudo ./script/manage-service.sh stop
• Restart service: sudo ./script/manage-service.sh restart
• Check status: sudo ./script/manage-service.sh status
• View logs: sudo ./script/manage-service.sh logs
• Uninstall service: sudo ./script/manage-service.sh uninstall

Windows Specific

Run all commands from an elevated PowerShell prompt:

# Install service
.\script\manage-service.ps1 install

# Start service
.\script\manage-service.ps1 start

# View logs
.\script\manage-service.ps1 logs

Directory Structure

The server requires the following directory structure:

.
├── build/               # Compiled binaries
├── config/              # Configuration files
│   ├── config.json      # Main configuration
│   └── certs/           # TLS certificates (if using TLS)
├── logs/                # Log files (created automatically)
│   ├── output.log       # Standard output
│   └── error.log        # Error output
└── script/              # Management scripts

Advanced Configuration

Log Rotation

Logs are automatically rotated when they reach 100MB. To configure:

1. Edit config/config.json:

{
  "Logging": {
    "MaxSizeMB": 100,
    "MaxBackups": 5,
    "MaxAgeDays": 30
  }
}

Rate Limiting

Configure rate limiting in config/config.json:

{
  "RateLimiting": {
    "RequestsPerMinute": 100,
    "BurstLimit": 20,
    "ExemptIPs": ["127.0.0.1"]
  }
}

TLS Configuration

To enable TLS, provide certificate files in config/certs/ and update:

{
  "Listeners": [
    {
      "host": "0.0.0.0",
      "port": "465",
      "encryption": "tls",
      "require_auth": true
    }
  ],
  "TLSCertFile": "certs/cert.pem",
  "TLSKeyFile": "certs/key.pem"
}

Troubleshooting

Common Issues

1. Service fails to start

   • Verify configuration file exists and is valid
   • Check logs: sudo ./script/manage-service.sh logs
   • Ensure required ports are open

2. Permission denied errors

   • Run commands with sudo/Administrator privileges
   • Verify installation directory permissions

3. Connection issues

   • Verify firewall settings
   • Check network connectivity
   • Validate TLS certificates (if using)

License

MIT License