Some suggestions for spam filter:
1. options to filter e-mail addresses with N - digits in alias or domain part.
2. options to filter malformed addresses i.e. without domain
3. to: field is blank (it must be an option, there are some problems with charsets)
4. to: and from: are the same
5. group country filter NOT but countries itself but to charset groups i.e cyrrilic, chinese simplified, arabic, thai, turkish