I've changed to this :
smtpd_milters = inet:localhost:12768 unix:/var/spool/postfix/ctmilter/ctmilter.sock
non_smtpd_milters = inet:localhost:12768 unix:/var/spool/postfix/ctmilter/ctmilter.sock
After, I restart in Plesk : Milter de Plesk (Postfix)
and the service : Serveur SMTP...