Marat's Notes

KumoMTA is a modern, high-performance mail transfer agent (MTA) designed for high-volume email sending. This guide will walk you through the process of setting up and configuring KumoMTA for optimal performance and deliverability.

Prerequisites

Before beginning the installation, ensure you have:

System Requirements:
- Linux-based operating system (Ubuntu 20.04+ recommended)
- Minimum 4GB RAM
- 20GB+ disk space
- Static IP address
- Proper DNS configuration
DNS Configuration:
- Valid SPF record
- DKIM setup
- DMARC policy
- Reverse DNS (PTR) record

Installation

1. System Preparation

First, update your system and install dependencies:

# Update system packages
sudo apt update && sudo apt upgrade -y

# Install required dependencies
sudo apt install -y \
    build-essential \
    libssl-dev \
    pkg-config \
    git \
    curl \
    wget

2. Installing KumoMTA

Download and install KumoMTA:

# Download the latest release
wget https://github.com/KumoCorp/kumomta/releases/latest/download/kumomta.deb

# Install the package
sudo dpkg -i kumomta.deb

Configuration

1. Basic Configuration

Create the main configuration file:

-- /opt/kumomta/etc/policy/init.lua
kumo.on('init', function()
  -- Configure logging
  kumo.configure_logging({
    level = 'INFO',
    format = 'json',
    destination = '/var/log/kumomta/main.log'
  })

  -- Configure SMTP listener
  kumo.start_esmtp_listener {
    listen = '0.0.0.0:25',
    hostname = 'mail.yourdomain.com',
    max_message_size = '50MB'
  }
end)

2. Queue Configuration

Set up the message queue:

-- /opt/kumomta/etc/policy/queue.lua
kumo.on('queue_message', function(msg)
  -- Set default queue parameters
  msg:set_meta('queue', 'default')
  msg:set_meta('retry_interval', '5m')
  msg:set_meta('max_retries', 3)
end)

3. DKIM Configuration

Configure DKIM signing:

-- /opt/kumomta/etc/policy/dkim.lua
kumo.on('smtp_server_message_received', function(msg)
  -- Load DKIM key
  local dkim_key = kumo.load_dkim_key {
    domain = 'yourdomain.com',
    selector = 'default',
    key_path = '/opt/kumomta/etc/dkim/private.key'
  }

  -- Sign the message
  msg:dkim_sign(dkim_key)
end)

Performance Tuning

1. Resource Allocation

Optimize system resources:

-- /opt/kumomta/etc/policy/performance.lua
kumo.on('init', function()
  -- Configure worker threads
  kumo.configure_workers {
    count = 4,  -- Adjust based on CPU cores
    max_connections = 1000
  }

  -- Configure memory limits
  kumo.configure_memory {
    max_heap_size = '2GB',
    max_message_size = '50MB'
  }
end)

2. Rate Limiting

Implement rate limiting:

-- /opt/kumomta/etc/policy/rate_limiting.lua
kumo.on('smtp_server_message_received', function(msg)
  -- Rate limit by domain
  local domain = msg:get_meta('domain')
  if not kumo.rate_limit(domain, {
    max_requests = 100,
    window = '1m'
  }) then
    return kumo.reject(550, 'Rate limit exceeded')
  end
end)

Monitoring and Logging

1. Log Configuration

Set up comprehensive logging:

-- /opt/kumomta/etc/policy/logging.lua
kumo.on('init', function()
  kumo.configure_logging {
    level = 'INFO',
    format = 'json',
    destination = '/var/log/kumomta/main.log',
    rotation = {
      max_size = '100MB',
      max_files = 10
    }
  }
end)

2. Metrics Collection

Configure metrics collection:

-- /opt/kumomta/etc/policy/metrics.lua
kumo.on('init', function()
  kumo.configure_metrics {
    destination = 'prometheus',
    port = 9090,
    path = '/metrics'
  }
end)

Security Configuration

1. TLS Configuration

Set up TLS for secure communication:

-- /opt/kumomta/etc/policy/tls.lua
kumo.on('init', function()
  kumo.configure_tls {
    certificate = '/opt/kumomta/etc/tls/cert.pem',
    private_key = '/opt/kumomta/etc/tls/key.pem',
    protocols = {'TLSv1.2', 'TLSv1.3'}
  }
end)

2. Access Control

Implement access control:

-- /opt/kumomta/etc/policy/access.lua
kumo.on('smtp_server_message_received', function(msg)
  local client_ip = msg:get_meta('client_ip')
  
  -- Check against allowlist
  if not kumo.is_allowed_ip(client_ip) then
    return kumo.reject(550, 'Access denied')
  end
end)

Testing and Validation

1. Basic Testing

Test the configuration:

# Check configuration syntax
sudo kumomta check-config

# Test SMTP connection
telnet localhost 25

# Send test email
echo "Subject: Test" | sendmail -f sender@yourdomain.com recipient@example.com

2. Monitoring Setup

Set up monitoring:

# Install monitoring tools
sudo apt install -y prometheus node-exporter

# Configure Prometheus
cat > /etc/prometheus/prometheus.yml << EOF
scrape_configs:
  - job_name: 'kumomta'
    static_configs:
      - targets: ['localhost:9090']
EOF

Troubleshooting

Common issues and solutions:

Connection Issues:
- Check firewall settings
- Verify DNS configuration
- Check network connectivity
Delivery Problems:
- Verify SPF/DKIM/DMARC records
- Check IP reputation
- Review bounce messages
Performance Issues:
- Monitor system resources
- Check queue status
- Review rate limits

Conclusion

Setting up KumoMTA requires careful attention to configuration, security, and performance tuning. By following this guide, you’ll have a robust, high-performance email server capable of handling high-volume email sending while maintaining good deliverability rates.

Remember to:

Regularly monitor system performance
Keep software updated
Maintain security configurations
Monitor email deliverability metrics
Review and adjust rate limits as needed

With proper configuration and maintenance, KumoMTA can provide a reliable and scalable solution for your email sending needs.

Setting up KumoMTA: A High-Performance Email Server