QMAIL restart
/etc/init.d/qmail restart

QMAIL – messages per IP
/etc/xinetd.d/smtp_psa and /etc/xinetd.d/smtps_psa
http://glomerate.wordpress.com/category/plesk/
added this:
instances = 10
per_source = 1
server = /var/qmail/bin/tcp-env