Emailing your massage clients periodically should be a given, like Marketing 101. You can send them monthly tips about health or something interesting, and you can also let them know your upcoming openings or changes in your schedule. But how do you do that without emailing each person individually?
An email marking service is the best way to go. You can either use plain text for a simple email (apparently, your clients’ inboxes are less likely to send them to spam that way. Read more about that here). You can also design something nice (which is what we do) that will mesh with your website.
We are going to skip over the paid versions because if you’re just learning about this now, a free version will probably suffice nicely.