After you have fixed the PID problem, you'll notice that "service postgrey restart" still does nothing. To fix it:

# nano /etc/init.d/postgrey

comment out almost everything in the do_stop section, and limit it to just these two lines:

kill `ps aux | grep postg | egrep -v "(restartpostgrey|grep)" | cut -d " " -f 2`
rm -f $PIDFILE