The Extranet provides the option to display a "Notify me about special offers" checkbox on the checkout page of the booking engine. This checkbox allows the Hotel to save the guest's email for marketing purposes. Below is an example of how it appears on the booking engine. 

With:

Instructions to Enable

Step 1: On the Extranet, under the Booking Engine tab select on General Settings

Step 2: Select on Booking Engine Settings

Step 3: Under the Show "Notify me about special offers" checkbox on Checkout make your selection and be sure to Save when finished.