E-mail comment reply notice to others

Is there a plug-in or setting I can use to send e-mail notification to the people who comment on my blog posts when someone else posts a comment under theirs (like a response)?

I’ve been looking for a while now, and am surprised it is so hard to find information on this functionality. Thanks for any advice you can give.

– Iain Hamp
https://www.rocketmouse.com