I don't use the openldap server, in fact I'm using an other host with Active Directory server. Do you think the limit comes from Active directory and not python ?

The limit issue is almost 100% coming from AD. Active Directory limits the results of an LDAP query. The following article states it's 10,000 by default. It also tells you how to increase it: http://support.microsoft.com/default.aspx?scid=kb;en-us;243281 Hope this helps. Regards, Andy.