Note: this feature availability depends on your plan.

Hide from Address Book is an option which allows the Administrator to hide an object from the Address Book.
Note: If an object is hidden from the address book, the mailbox will not be visible in the Global Address List. Names which are not visible in the address book cannot be found by services or features that rely on the Global Address List, such as the Auto-complete feature and Outlook Profile Helper. The Profile Helper relies on the Global Address List to create a profile and cannot be used for any mailbox that has been hidden from the address book.
To hide an Exchange mailbox:
  1. Navigate to Services > Mailboxes > Exchange Mailboxes
  2. Click on the Display Name of the mailbox you want to hide
    Find the mailbox
  3. Under Exchange, click Advanced Settings
  4. Check the Hide from address book box and click Save Changes
    Hide from GAL
To hide a Distribution List, a Company Contact or a Resource Mailbox from the Address Book:
  1. Find the object on the corresponding tab
  2. Click on the Display Name
  3. Click Hide from address book
    Hide DL, contact or resource mailbox from GAL