Greylisting in spamd

Spamd does greylisting by running on a host with (initially) all smtp connections redirected to the spamd daemon.

table <spamd-white> persist
rdr pass inet proto tcp from !<spamd-white> to any port smtp -> 127.0.0.1 port 8025

Spamd greylisting uses a db file (/var/db/spamd) to store the greylist tuples and some other pertiniant information. 

Spamd whitelists connections by adding them to the spamd-white pf table. hosts in this table do not get redirected. Whitelist entries are removed from the table when they expire