ok i got it
In FreeBSD you have to add saslauthd_flags in /etc/rc.conf:
cat /etc/rc.conf |grep saslauthd
saslauthd_flags="-a pam -r"
'-r' is the winner
-r Combine the realm with the login before passing to authentication mechanism
Ex. login: "foo" realm: "bar" will get passed as login: "foo@bar"
The realm name is passed untouched.
By default saslauthd rc script (/usr/local/etc/rc.d/saslauthd) run saslauthd with '-a pam' argument. There is no saslauthd main config file. Only auth via LDAP use config file:
/var/run/saslauthd/mux The default communications socket.
The default configuration file for ldap support.
it was just too simple