Each time you visit the site, you'll see yellow flags next to forums that have had postings since your last visit. The same is true for the posts in the forums. Unless you completely clear the history in your internet browser, you should see new posts when you visit next time.
I do what Ingy does regarding posts and just look for the flags; I don't rely on th email notifications anymore because I wasn't getting them consistently. And my email inbox is much cleaner now, too