You are right. In KB 1711 sendmail is in /var/qmail/bin, but I haven't. Sendmail is in /usr/sbin. Can I replace the /var/qmail/bin / with /usr/sbin/ ?
Edit:
FYI I have Plesk Panel 11.0.9 and see in "Services management"-> "Pelsk milter (Postfix)" and "SMTP Server (Postfix)". So it looks that...