GeoIP

If milter-greylist was built with support for GeoIP (—with-libGeoIP) it's possible to e.g. greylist based on country of origin.

Example from greylist.conf that would greylist mail from Russia:

geoipdb "/usr/share/GeoIP/GeoIP.dat"

racl greylist geoip "RU" delay 3h

Or create a list of countries you want to grey/blacklist:

list "delayed_countries" geoip { \
   "RU" \ # Russia
   "CN" \ # China
}

racl greylist list "delayed_countries" delay 3h

More info on the GeoIP application can be found here: http://www.maxmind.com/app/api