Solution for Postfix (Score 5)

If not active in /etc/postfix/main.cf uncomment the line and change it to a line similar to:

header_checks = regexp:/etc/postfix/header_checks

Add the following line in /etc/postfix/header_checks:

/^Subject: ILOVEYOU/ REJECT

This will reject mails containing this subject.

Thanks to Claus Guttesen who posted this on the postfix mailling list.