Use something like
for i in `mysql -uadmin -p\`cat /etc/psa/.psa.shadow\` psa -Ns -e "select concat(mail.mail_name,\"@\",domains.name) as address from mail,domains,accounts where mail.dom_id=domains.id and mail.account_id=accounts.id order by address"`; do /usr/local/psa/bin/spamassassin -u $i -status true; done