Starting with OpenBSD 4.1, you can sync greylists
spamd command line flags:
-Y sync target
-y sync listener
on mainoffice-gw.example.com
-Y minorbranch-gw.example.com -y re0
on minorbranch-gw.example.com
-Y mainoffice-gw.example.com -y re0
Also, exporting your spamd-greytrap list to text is a grep + awk oneliner