Disable Exchange resource booking

Launch Exchange Management Shell (PowerShell). Type in the following command to check the current policies assigned to the resource:

get-calendarprocessing -identity "ResourceName" | fl *policy*

You will see results similar to these:

RequestOutOfPolicy    : {}
AllRequestOutOfPolicy : True
BookInPolicy              : {}
AllBookInPolicy          : True
RequestInPolicy         : {}
AllRequestInPolicy     : False

To disable booking for the resource type in the following command:

set-calendarprocessing -identity "ResourceName" -allbookinpolicy:$false

*ResourceName is the actual name of the resource mailbox