Email when replied

How do you make all posts by all members on phpbb that reply to your post send a email notification by default is there a plugin that does that or do I have to edit the functions.php file?

I want people to get emails when someone replies to their posts

im asking here because i noticed this forum has it enabled by default so when my topic gets a reply i receive an email

[IvanPF]

This website, although it uses phpBB as its backend, is heavily modified. As far as I know, phpBB only sends notifications if you're subscribed to the topic, and I'm not aware of any extensions that do that, though I suppose it's possible.

[IvanPF]

I found this extension that I think does what you need, but I haven't tested it.
https://github.com/dmzx/Notify-upon-reply