To create a listing group, browse to the "Settings" page.
Choose "Listing Groups" from the menu on the left.
Press the blue "Add Group" button
Add the listings you would like to the listing group from the drop-down under "Add Listings."
Click the "Save" button.
You will now see the listing group available under the "Messaging" menu at the top of the Host Tools dashboard. Any message rules added to this listing group will be sent to guests staying at any of the listings in the listing group.