https://news.ycombinator.com/threads?id=joering2
There's also an older thread that mentions somebody implementing something like this using the hnrss service, but I'm not sure if that's even still up or not.
https://news.ycombinator.com/threads?id=joering2
https://news.ycombinator.com/threads?id=FOLLOWEDUSER
you can write a cron to step through a list of usernames ; pack each one into a URL; scrape it and do a sendmail