Synspam uses Netfilter NFQUEUE to catch the source IP address of any machine connecting to your mail server, running multiple tests against it (RBL check, regexp on the reverse name, etc.) before forwarding the connection to the MTA. In order to have as few false positives as possible, a scoring system is used. If the source IP address is believed to be a spammer IP address, the connection can be dropped. There is a dry run mode if you just want to test it, which is the default.
ufdbGuard is a URL filter. The URL filter blocks access to sets of Web sites and cooperates with the Squid proxy. It integrates with LDAP, Kerberos, Active Directory, MySQL, and others to define different ploicies for different groups of users. ufdbGuard also enforces SafeSearch for many search engines, blocks Skype, UltraSurf, Tor, unsafe HTTPS sites, and dynamically detects proxy tunnels. The multi-threaded daemon uses a fast algorithm that does 50,000 URL verifications per second on an Intel Core 2 Duo (Conroe) at 2.4 GHz.