SpamAssassin MCP Server

A secure, containerized Model Context Protocol (MCP) server that integrates SpamAssassin for defensive email security analysis. This server provides Claude Code with comprehensive email analysis capabilities while maintaining strict security boundaries.

🛡️ Security-First Design

Defensive Operations Only - This server exclusively provides security analysis capabilities:

• ✅ Email spam detection and analysis
• ✅ Sender reputation checking
• ✅ Rule testing and validation
• ✅ Configuration inspection
• ❌ NO email sending/relay capabilities
• ❌ NO malicious content generation
• ❌ NO offensive security tools

🚀 Quick Start

Prerequisites

• Docker and Docker Compose
• Claude Code with MCP support

1. Build and Start

# Clone or create the project directory
cd spamassassin-mcp

# Optional: Copy and customize configuration
cp .env.example .env
# Edit .env to customize ports and settings

# Build and start the containers
docker compose up -d

# Check health
docker compose logs spamassassin-mcp

1. Alternative: Use Pre-built Image

# Pull the latest image from Docker Hub
docker pull your-dockerhub-username/spamassassin-mcp:latest

# Run the container
docker run -d \
  --name spamassassin-mcp \
  -p 8081:8080 \
  your-dockerhub-username/spamassassin-mcp:latest

2. Connect Claude Code

# Connect to containerized server (SSE transport)
# Server URL: http://localhost:8081/mcp

# Or for direct connection (stdio transport)
./mcp-server

3. Test the Integration

# Scan a sample email
/scan_email --content "Subject: Test Email

This is a test email for spam analysis."

# Check sender reputation
/check_reputation --sender "test@example.com"

# Get current configuration
/get_config

🔧 Available Tools

Email Analysis

scan_email

Analyze email content for spam probability and rule matches.

Parameters:

• content (required): Raw email content including headers
• headers (optional): Additional headers to analyze
• check_bayes (optional): Include Bayesian analysis
• verbose (optional): Return detailed rule explanations

Example:

{
  "content": "Subject: Urgent Action Required\\n\\nClick here to claim your prize!",
  "verbose": true,
  "check_bayes": true
}

check_reputation

Check sender reputation and domain/IP blacklists.

Parameters:

• sender (required): Email sender address
• domain (optional): Sender domain
• ip (optional): Sender IP address

explain_score

Explain how a spam score was calculated with detailed breakdown.

Configuration Management

get_config

Retrieve current SpamAssassin configuration and status.

update_rules

Update SpamAssassin rule definitions (defensive updates only).

Parameters:

• source (optional): Rule source (official/custom)
• force (optional): Force update even if recent

Rule Testing

test_rules

Test custom rules against sample emails in a safe environment.

Parameters:

• rules (required): Custom rule definitions
• test_emails (required): Array of sample emails to test

📁 Project Structure

spamassassin-mcp/
├── main.go                 # MCP server entry point
├── go.mod                  # Go module definition
├── Dockerfile              # Multi-stage container build
├── docker-compose.yml      # Service orchestration
├── internal/
│   ├── config/            # Configuration management
│   ├── handlers/          # MCP tool handlers
│   └── spamassassin/      # SpamAssassin client wrapper
├── configs/
│   └── config.yaml        # Server configuration
├── scripts/
│   ├── entrypoint.sh      # Container initialization
│   └── health-check.sh    # Health monitoring
└── README.md

⚙️ Configuration

Environment Variables

Variable	Default	Description
SA_MCP_HOST_PORT	8081	Host port for container deployment
SA_MCP_LOG_LEVEL	info	Logging level (debug, info, warn, error)
SA_MCP_SERVER_BIND_ADDR	0.0.0.0:8080	Server bind address (container internal)
SA_MCP_SPAMASSASSIN_HOST	localhost	SpamAssassin daemon host
SA_MCP_SPAMASSASSIN_PORT	783	SpamAssassin daemon port
SA_MCP_SPAMASSASSIN_THRESHOLD	5.0	Spam score threshold
SA_MCP_SECURITY_MAX_EMAIL_SIZE	10485760	Max email size (10MB)
UPDATE_RULES	false	Update SpamAssassin rules on startup
MCP_TRANSPORT	auto	Transport mode (auto, stdio, sse)

Security Settings

The server includes comprehensive security measures:

• Rate Limiting: 60 requests/minute with burst of 10
• Input Validation: Email format and size validation
• Content Sanitization: Safe handling of email content
• Container Security: Non-root execution, read-only filesystem
• Network Isolation: Custom bridge network
• Resource Limits: Memory and CPU constraints

🔍 Usage Examples

Basic Email Scanning

# Simple spam check
/scan_email --content "$(cat suspicious_email.eml)"

# Detailed analysis with Bayes
/scan_email --content "$(cat email.eml)" --verbose --check_bayes

Reputation Analysis

# Check sender reputation
/check_reputation --sender "unknown@suspicious-domain.com"

# Check domain and IP
/check_reputation --domain "suspicious-domain.com" --ip "192.168.1.100"

Rule Development

# Test custom rules
/test_rules --rules "header LOCAL_TEST Subject =~ /test/i
describe LOCAL_TEST Test rule
score LOCAL_TEST 2.0" --test_emails '["Subject: test email\n\nThis is a test."]'

Score Analysis

# Get detailed score explanation
/explain_score --email_content "Subject: Free Money!\n\nClaim your prize now!"

🏥 Health Monitoring

Health Check Endpoint

The container includes automated health checks:

# Check container health
docker-compose exec spamassassin-mcp /usr/local/bin/health-check.sh

# View health status
docker ps

Logs and Monitoring

# View server logs
docker compose logs -f spamassassin-mcp

# Monitor resource usage
docker stats spamassassin-mcp

# Test MCP connectivity (container mode)
curl -v http://localhost:8081/mcp

🔒 Security Considerations

Defensive Posture

• Server exclusively provides analysis capabilities
• No email transmission or relay functionality
• Input validation and sanitization on all endpoints
• Rate limiting to prevent abuse
• Comprehensive logging for audit trails

Container Security

• Runs as non-root user (spamassassin)
• Read-only root filesystem
• No new privileges allowed
• Resource limits enforced
• Network isolation

Data Handling

• No persistent storage of email content
• Temporary analysis only
• Configurable retention policies
• GDPR/privacy-compliant design

🚧 Development

Building from Source

# Install dependencies
go mod download

# Build binary
go build -o mcp-server main.go

# Run locally (requires SpamAssassin)
./mcp-server

Testing

# Run with testing profile (includes spamd)
docker compose --profile testing up -d

# Test SpamAssassin connectivity
docker compose exec spamassassin-mcp timeout 2 bash -c 'echo >/dev/tcp/localhost/783'

# Test MCP server health
docker compose exec spamassassin-mcp /usr/local/bin/health-check.sh

🔧 Troubleshooting

Common Issues

Container Restart Loop

Symptoms: Container continuously restarts with "read error: EOF"

• Cause: stdio transport expects stdin input in container environment
• Solution: Server automatically detects container mode and uses SSE transport
• Verification: Check logs show "Starting MCP server with SSE transport"

Port Conflicts

Symptoms: "bind: address already in use"

• Solution: Modify SA_MCP_HOST_PORT in .env file
• Default: Server uses port 8081 to avoid conflicts

Network Subnet Conflicts

Symptoms: "Pool overlaps with other one on this address space"

• Solution: docker-compose.yml uses 192.168.100.0/24 network
• Customization: Modify networks section if conflicts persist

Health Check Failures

Symptoms: Container marked unhealthy

• Verification: Run /usr/local/bin/health-check.sh manually
• Common Fix: Ensure SpamAssassin daemon is running
• Debug: Check docker compose logs spamassassin-mcp

📚 Documentation

• API Reference - Complete MCP tools documentation
• Deployment Guide - Production deployment instructions
• Security Guide - Security architecture and best practices
• Development Guide - Contributing and development setup
• Configuration Reference - Complete configuration options

📄 License

MIT License - See LICENSE file for details.

🔄 CI/CD with GitHub Actions

This project uses GitHub Actions for continuous integration and deployment:

1. Docker Build and Push: Automatically builds and pushes Docker images to Docker Hub on pushes to main branch and tags
2. Test Docker Image: Runs tests on the Docker image to ensure it builds and runs correctly
3. Update Docker Hub Overview: Automatically updates the Docker Hub repository description when README.md changes

Setting up Docker Hub Publishing

To use the Docker Hub publishing workflow:

1. Create a Docker Hub account if you don't already have one

2. Generate a Docker Hub access token:

   • Log in to Docker Hub
   • Go to Account Settings > Security
   • Click "New Access Token"
   • Give it a descriptive name (e.g., "GitHub Actions")
   • Set permissions to "Read & Write"
   • Copy the generated token (you won't see it again)

3. Set up Docker Hub credentials as GitHub Secrets:

   • Go to your GitHub repository settings
   • Click "Secrets and variables" > "Actions"
   • Add two new repository secrets:
     • DOCKER_USERNAME: Your Docker Hub username
     • DOCKER_PASSWORD: Your Docker Hub access token (the token you just created)

4. Push to the main branch or create a tag starting with v (e.g., v1.0.0)

   • The workflow will automatically build and push the image to Docker Hub

The published images will be available at https://hub.docker.com/r/YOUR_USERNAME/spamassassin-mcp where YOUR_USERNAME is your Docker Hub username.

Image tags:

• latest - Latest build from the main branch
• vX.Y.Z - Specific version tags for releases
• commit-SHA - Specific commit builds

Manual Docker Hub Overview Update

You can also manually generate the Docker Hub overview:

# Generate Docker Hub overview
./scripts/extract-dockerhub-info.sh

# Or use the manual update script with your credentials
./scripts/update-dockerhub-manual.sh your-docker-username your-docker-access-token

🤝 Contributing

Contributions welcome! Please read our Contributing Guide and ensure all changes maintain the security-first, defensive-only design principles.

📞 Support

For issues and questions:

1. First Steps: Check the Troubleshooting Guide
2. Logs: docker-compose logs spamassassin-mcp
3. Health Check: docker-compose exec spamassassin-mcp /usr/local/bin/health-check.sh
4. SpamAssassin Status: docker-compose exec spamassassin-mcp pgrep spamd

🔗 Related Projects

• Model Context Protocol - Official MCP specifications
• Claude Code - Claude's official CLI
• SpamAssassin - Open source spam filtering

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⚠️ Security Notice: This server is designed exclusively for defensive security analysis. It does not provide capabilities for sending emails, generating spam content, or any offensive security operations. All operations are logged and auditable.