From this answer and the docs I know that /users/:id and /users exist, and include=email can be used to append the email address.
However in a large account, neither retrieving individual users or trawling through every user seems like a good solution for a course with 1000 users.
What is the best way to get the default email addresses for those in a course? The enrollments API returns users, but the include email query parameter does not work. (edit: this would be the ideal result, if enrollments returned the email)
The /courses/:id/users API would be another solution but it appears to append the default email for just users who are not pending?