Answer: This article will show you how to hide a user mailbox from Exchange global address lists, this is very useful when we want to hide a test email address or an employee that is no longer working for the company.
To hide a Mailbox from the address list follow the steps below:
Open EMC -> Recipient Configuration ->mailbox
Locate the mailbox that you want to hide and double click on it.
In the General tab tick the box, Hide from Exchange Address Lists
Click OK and Apply, the settings will replicate to all Outlook clients.