Sympa 3.3.3 and LDAP

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I've just install sympa 3.3.3 on a LINUX MANDRAKE 8.1 in a Intranet 
Environement. LDAP Authentication is a very important feature for my project.

I've got an authentication problem with UID. 
The syslog tells me that that "there is no entry in the ldap directory tree".
The ldap directory works fine ( I've tried a ldap request via a browser ).

I think there is a problem with in auth.conf file.
the ldap server name is : toto.intra.psa
port number :389
organistation is : o=psa
organisational unit is : ou=users

Please, I need help to correctly write the auth.conf file.

Thanks.

Patrick FORT