aryeh, click the Profile tab at the top, then under Modify Profile, click on Notifications. There are several options to choose from regarading boards or topics where you have posted a message.
Also, you can individually subscribe to any board or topic (even if you haven't posted a message in it). When you have a topic open, look near the Reply button (not Quick Reply). Just above and just below the message thread, there is a row of buttons. (The row of buttons is justified to the right.) One of them is a "Notify" button. (Besides Reply and Notify, there's also Add Poll, Print, and some others.) If you click Notify, you'll get an email every time a new message is posted in whatever topic you have open.
To be notified for any new message in a particular board, open the board index, and you can find the same Notify button, in approx the same place.