you might want to hide a mailbox so that it doesn’t appear in the global address list or other address lists. One reason for doing this is if you have administrative mailboxes that you use only for special purposes.
To hide a mailbox from the address lists, follow these steps:
1. Open the Properties dialog box for the mailbox-enabled user account by double-clicking the user name in the Exchange Management Console.
2. On the General tab, select the Hide From Exchange Address Lists check box and then click OK.