I can find no documentation on this - How does this work ?
ZEXTRAS ADDRESS BOOK FOR MS OUTLOOK/MAC MAIL/ THUNDERBIRD
(NEW) - Sep 2020
Connect Microsoft Outlook, Thunderbird and Mac Mail to your centralized Zimbra GAL and address books to achieve a complete client experience.
The Address Book can work either in conjoint with IMAP/ POP or EAS.
Microsoft Outlook can leverage on EAS and Address Book to provide a full Outlook connector experience without any plugin on the client!