VPOP3 supports a Global Address Book. This allows users to access a centralised directory of contacts, for details such as their email addresses.
Email clients can read the Address Book using an Internet protocol called LDAP (Lightweight Directory Access Protocol). LDAP has some serious flaws when it comes to updating/writing directory entries, so neither email clients nor VPOP3 supports that facility using LDAP. LDAP was designed for huge centralised address books which would be managed from a central location, not as a shared contact system which would be updated by many different users, possibly simultaneously, but LDAP is the most widely supported protocol in email clients.
Users can also access the VPOP3 Address Book using their Webmail facility.
Email clients usually support LDAP, but they can support it in various ways so not all email clients may use it in all the possible ways:
•The most basic email clients will only allow manual searches for addresses.
•Some will allow scrolling through the entire address book list using some LDAP paging/sorting extensions which VPOP3 supports.
•Some will perform address completion when typing in the To/Cc address fields of an email.
LDAP is a hierarchical database system which may cause some confusion for people not used to it. In most LDAP client implementations, there is a setting called 'Base DN'. This tells it the 'root' of the hierarchical tree that searches will occur from. With VPOP3 this can be set to either <blank> or 'O=VPOP3' to include the whole LDAP database (the most common usage), but can be specified differently to reduce the scope of LDAP searches. For instance, 'OU=External,O=VPOP3' will tell the email client to just search in the externally added address book entries, not the ones automatically added by VPOP3 for local users.
The basic hierarchical tree is shown below. Note that when entering a Base DN you specify the parts in reverse order - eg 'OU=USERS,OU=Internal,O=VPOP3' rather than 'O=VPOP3,OU=Internal,OU=Users'
O=VPOP3 -- OU=Internal -- OU=USERS -- UID=<username> (internal user)
| -- OU=LISTS -- UID=<listname> (internal list)
-- OU= External -- OU=VPOP3 -- owner=0 -- UID=<id number> ('global address book' entry)
| -- owner=<owner user ID> -- UID=<id number> (user's personal address book entry)
| -- cat=<extra directory ID> -- UID=<id number> (VPOP3 Enterprise only - user's secondary personal address book entry)
-- OU=ODBC (VPOP3 Enterprise only - ODBC address book)
In VPOP3 Enterprise, users can create multiple directories themselves which can be shared with other users. These appear as the cat=x,owner=y,OU=VPOP3,OU=External,O=VPOP3 entries above. This means that the LDAP client configuration can be configured to just look in these places.