The following Cypher statement can be used to get a list of email addresses for a mail merge announcement email.
MATCH (c:Course {slug: $slug})<-[:INTERESTED_IN]-(u)
WHERE coalesce(u.unsubscribed, false) = false
WITH c.interested AS interested, collect(u.email) AS emails
UNWIND emails AS email
WITH email WHERE email contains '@'
RETURN distinct email