Select and message a custom group of customers from the Customers page - simply select which customers you would like to contact from the list then click Actions > Message.

Message all the customers booked in to a session or course by navigating to the session on your Schedule or course in the Courses tab > clicking Attendees or Customers respectively > Message attendees.

You can also message all the customers with a certain package by going to Packages > select the relevant package > Package customers > Message.