Content-based
- Address Blacklist/Whitelist
- Content filtering
- Bayesian
- URL database
- Challenge/Response
- IBF (intent based filtering)
IP/Host-based
- RBL (realtime blackhole list)
- RPDNS (reverse path dns lookup)
- MX Lookup
- Greylisting
Pattern-based
- DCC (distributed checksum clearinghouse)
- RPD (recurrent pattern detection)
- SLS (statistical lookup service)
Did I miss any? If so, please let me know via the contact form. At a later time I will write articles based on each of the spam catching techniques.