If you mean getting an e-mail sent to you when someone has replied to a post you have started or replied on.
I think I read somewhere that since getting the new server, this 'service' is no longer an automatic thing - it was generating a lot of work for the server to send out emails etc especially given how popular some posts are. I think he said that it was slowing the system down too.
Hope that is the answer to the question you were asking.
a