InetOrgPerson is a ‘pure‘ X500 LDAP object class for a person as defined in
RFC2798 .
The User object class on the other hand is Microsofts own definition for a
person which has extensions which only work in Microsoft Active Directory.
If you wanted your Active Directory to communicate with other RFC compliant
directories the InetOrgPerson object class may be a better object to use
rather than the User object class.
原文：http://www.cnblogs.com/wuyuxiang/p/5166649.html