Once you engage for example by creating an idea or comment, you will automatically be subscribed for further updates for new comments or changes to your idea (if the Wiki feature is turned on).
You can also subscribe to each contribution by clicking the "Subscribe via email" button below each contribution.
In your profile page you have all your subscription listed and can easily unsubscribe from a specific idea.
Go to your profile page under "My Account > my dasboard". Here all your subscriptions are listed and you can easily unsubscribe by clicking the unsubscribe button.
Once you engage for example through an idea or comment, you will automatically receive emails for next activities by other users. Or you can subscribe to contributions by clicking the "Subscribe via email" button.