I was looking for free Antispam GW for my lab and I came accross Comodo Antispam Gateway. It is free for 1 domain and 10 users.
Sign up for free license is here:
Why to use this GW?
- Easy configuration
- Access via Admin interface
- Quarantine, blocklist, whitelist – all accessible with free license
- AD synchronization newly created also for free license!
Few screen shots: