To use an Active Directory (AD) as LDAP directory for Notes mail addressing you can use a Directory Assistance LDAP Document.
To query the AD Global Catalog you have to configure 3268 as LDAP port.
AD always needs a search base to query. If you want to retrieve mail users the search base is something like ‚cn=mail,cn=domain,cn=net'(or de…) if you want to retrieve all users don’t use cn=mail.
LDAP Directory Assistance allows Notes mail user to complete recpients name by pressing F9. The recipients name is then searched in the AD. Type Ahead and Select Addresses Dialog is not supported through LDAP Directory Assistance.
To enable Type Ahead and Select Addresses Dialog against an AD you need an LDAP account document in the users local addressbook.