Microsoft has removed this option from the GUI (ECP)
You must use Exchange Management Shell (EMS):
Set-MailContact -HiddenFromAddressListsEnabled $true
To confirm this actually worked you can run the following command from EMS.
Get-MailContact | fl *hidden*
If you need to revert your change just flip the Boolean back to $false
Set-MailContact -HiddenFromAddressListsEnabled $false
Обговорити
