There used to be a service called "HNNotify" which gave you the option of being emailed whenever someone replied to you. It was brilliant.
I think I remember seeing something from the mods, or paraphrasing the mods, that said something like: "We don't want people to get only involved in their own conversations, and we are concerned that a notification system will bias people towards not reading widely, and just reading things they've directly contributed to."
My memory may be faulty, and that might be wrong, but I seem to recall something like it.
Personally, I used HNNotify and lament its demise. I'm idly considering scripting a personal replacement- for me it wouldn't be worth the significant investment in time and effort to make something robust enough for general use. Perhaps someone might create a new version.
Edit: I see the comment[0] from dangrossman[1] mentions a replacement for HNNotify - I might give that a try.
I've always what kind of volume you do in terms of number of users or notifications?
Finding the new reply in a thread like this post I made the other day becomes a little tiresome: https://news.ycombinator.com/item?id=12302154.
If you use Chrome, Hacker News Enhancement Suite includes this feature.