I'm not sure if this option exists somewhere in the user settings, but most of the sites/forums that I get updates from directly in mail have the "If you don't want to view this, click here to unsubscribe from e-mail updates" option.
Cause sometimes you can read all the responses you got on a thread, and then few hours later you log in to your mail and you see all those mails about responses you already know you had and it fills up your e-mail. Plus if you get too many mails they may automatically go to the junk folder eventually.
Just an idea :)
