Increasing response on e-mail campaigns by keeping your list clean and importing new and fresh names regularly. Importing guests e-mails from the reservation system can be added to your e-mail service twice a year. You may want to segregate the list based on behavior: time of year they visited, or by type of business (wedding, group, reunion, etc.) Or better yet by behavior based on activities they participated in while at the property.
E-letter sign up on the web site is visible and the list grows through the site about 5% each month. Importing new guests e-mails would increase the response rate dramatically.