By default, each user has their own address book, but if you have a multi-user subscription, you can choose to have all users share a single address book. With a shared address book:
Only users with the role of Admin can perform this procedure.
Important: Once this setting is enabled, it cannot be undone. All users' address books will be permanently merged into one. There is no ability to go back to individual address books.
To enable the shared address book:
UPDATED: April 14, 2021