Microsoft Outlook 97 does not support the Lightweight Directory Access Protocol (LDAP) for client directory lookups. Microsoft Outlook 98 does support LDAP.

The Lightweight Directory Access Protocol (LDAP) is a protocol for clients to query and manage information in a Directory Service over a TCP connection (port 389). The LDAP protocol was designed by University of Michigan to provide access to the X.500 Directory while not incurring the resource requirements of the Directory Access Protocol (DAP). This makes it very suitable for use on the Internet.

Outlook 97 is not a LDAP client and does not provide the ability to query using LDAP. Active Directory is a Directory Service integrated with the Windows NT Server operating system; it offers the hierarchical view, extensibility, scalability, and distributed security required by all customers. Microsoft provides support for LDAP in Active Directory and enables it to integrate with the Internet. With this LDAP support, customers can deploy Active Directory in a corporate computing environment and interoperate with LDAP clients from multiple vendors.