You can use search in Outlook (Express) for the contacts of the company, have different groups, and have authority setup of groups.
You can limit the address books to be accessed to certain accounts or modify address books of certain groups.

Administrators can add address books for different groups such as the head office, branch offices, customers and suppliers, etc.
Administrators can decide who can share which groups address books.
Administrators can decide who can modify which address book for mutual maintenance and use of resources.
When sending mails via webmail, you can select the accessible contacts as recipients. List of address books of LDAP is established by administrators only.
LDAP shared address book supports authority management and division of labor maintenance. LDAP supports backup and restore and automatically backups daily.