I run OSX Server on a mac mini and was perusing /var/log/system.log and saw this odd error:
warning: problem talking to server private/policy: Undefined error: 0
postfix/spawn: warning: command /usr/bin/perl killed by signal 10
Just in case anyone else runs into this problem, I thought a little post here might save someone time. After some hunting around it turns out to be a corruption problem in the greylisting database. The private/policy is the call from the postfix main.cf to the greylisting script.
The fix is quite simple once you've tracked down the problem. First, turn off the mail service in Server app then open up a terminal window and type:
sudo rm /library/server/mail/data/mta/greylist.db
sudo rm /library/server/mail/data/mta/whitelist.db
And finally restart your mail service. The two files you just deleted store information for the greylist service and are recreated when not present. Now you shouldn't have all those errors in your log files and greylisting should be happy again.