The option that you need to set is "Default Thread Subscription Mode" in User Options in the User Control Panel. If you set it to "Do not subscribe" you won't get emails. You can also set it manually for each thread in which you post if you wish to override your default settings.
Of course that won't change the threads to which you are already subscribed. To do that, you need to go User Control Panel...List Subscriptions and manually delete them.