It would be nice to have an (optional) global address book, either built implicitly by all users (of a directory) or fed from an LDAP (or something else) server, that’s then automatically available to every user of a directory. In some sense having a “company directory”.
Further, some may also enjoy having a similar, but manually managed, global address list, e.g. frequently needed external contacts / customers. For that use case, I think it would be fine to limit editing permission to admins.
For large deployments, you don’t want an addressbook with all employees, because most clients cannot deal with 20000 or 100000 entries in the addressbook. Thunderbird surely cannot, we’ve tried. Also, even if it could, you’d see a lot of changes being synced all the time to all clients. Lastly, do you want to effectively send out a notification to all 100000 employees whenever anybody anywhere joins or leaves your company?
The better solution is a query-only directory, similar to Exchange GAL (“Global Address List”). When you type a name or address in the To: field of your mail composer, or your calendar invitee list, the autocomplete widget in the client not only searches the local address books, but also makes a query to the server. Thunderbird can do that with LDAP, Thunderbird with our Owl can do it with Exchange GAL, and Parula can do it with Exchange, and we’d love to implement support for JMAP query-only directories, once Stalwart implements a JMAP API and can query the upstream LDAP server (e.g. ActiveDirectory) in the backend.
That’s a fair point, an I was also thinking about something like GAL or an LDAP search-only directorry.