Stars are public - navigating to any GitHub profile and clicking the 'Stars' tab shows all the repositories starred by the user. Moreover, all users that have starred a repository can be viewed by appending /stargazers to the repo url or clicking the stars link in the sidebar.
minimaxir|4 years ago
If you really wanted to get GitHub data in bulk for illicit purposes and you know how to work with big data you can get it from the GitHub Archive but that’s a topic for another day. (Although it may not have user emails)