With postfix-2.9-RC2 on FreeBSD 8.1 I assume the "Operation not permitted" message is an artifact of writing to a disconnected socket or such and nothing to worry about? Only happens on a small percentage of connections rejected by postscreen.
So far today (not a particularly busy server): # grep 'postscreen.*DISCONNECT' /var/log/maillog | wc -l 1663 # grep 'postscreen.*Operation not permitted' /var/log/maillog | wc -l 3 Jan 25 05:01:39 mgate3 postfix/postscreen[47863]: CONNECT from [59.183.173.6]:20919 to [192.168.70.43]:25 Jan 25 05:01:45 mgate3 postfix/postscreen[47863]: DNSBL rank 10 for [59.183.173.6]:20919 Jan 25 05:07:04 mgate3 postfix/postscreen[47863]: COMMAND TIME LIMIT from [59.183.173.6]:20919 Jan 25 05:07:04 mgate3 postfix/postscreen[47863]: warning: write [59.183.173.6]:20919: Operation not permitted Jan 25 05:07:04 mgate3 postfix/postscreen[47863]: DISCONNECT [59.183.173.6]:20919 Jan 25 12:03:07 mgate3 postfix/postscreen[47863]: CONNECT from [46.249.0.102]:54843 to [192.168.70.43]:25 Jan 25 12:03:13 mgate3 postfix/postscreen[47863]: DNSBL rank 6 for [46.249.0.102]:54843 Jan 25 12:03:13 mgate3 postfix/postscreen[47863]: warning: write [46.249.0.102]:54843: Operation not permitted Jan 25 12:03:13 mgate3 postfix/postscreen[47863]: HANGUP after 0 from [46.249.0.102]:54843 in tests after SMTP handshake Jan 25 12:03:13 mgate3 postfix/postscreen[47863]: DISCONNECT [46.249.0.102]:54843 Jan 25 13:40:54 mgate3 postfix/postscreen[47863]: CONNECT from [88.72.223.26]:61053 to [192.168.70.43]:25 Jan 25 13:41:00 mgate3 postfix/postscreen[47863]: DNSBL rank 6 for [88.72.223.26]:61053 Jan 25 13:41:00 mgate3 postfix/postscreen[47863]: warning: write [88.72.223.26]:61053: Operation not permitted Jan 25 13:41:00 mgate3 postfix/postscreen[47863]: HANGUP after 0 from [88.72.223.26]:61053 in tests after SMTP handshake Jan 25 13:41:00 mgate3 postfix/postscreen[47863]: DISCONNECT [88.72.223.26]:61053 -- Noel Jones