You can only contact your customers if they have chosen to opt into receiving marketing emails from your hotel.
Whenever a customer is placing an order on the front end or a member of your team is placing an order on the back end, there will be a box to tick if they'd like to receive hotel info and offers. You can only contact them if this box has been ticked.
The customer's order details will also show whether they have opted in or not when an individual order has been opened in Gifted.