So you're using the Adding Greylisting support to qmail on Plesk 8|Greylisting support I linked to but you upgraded Plesk and BOOM Greylisting is gone and spam is back, eh? Not to fear! You did leave the source in place, right? If so, just run this script:

 #!/bin/sh
 
 cd /root/qmail-1.03
 make clean
 make
 
 /etc/rc.d/init.d/qmail stop
 
 cp -f qmail-envelope-scanner /var/qmail/bin/.
 cp -f qmail-smtpd /var/qmail/bin/.
 chown root.qmail /var/qmail/bin/qmail-envelope-scanner
 chown root.qmail /var/qmail/bin/qmail-smtpd
 
 /etc/rc.d/init.d/qmail start

I've been using this since Plesk 8 0 1 to update Greylisting after each Plesk update. YMMV.