[yorkieusa]

As Chachi said, it is in User CP, Edit Options, then this is what you're looking for:

Default Thread Subscription ModeWhen you post a new thread, or reply to a topic, you can choose to automatically add that thread to your list of subscribed threads, with the option to receive email notification of new replies to that thread.
Do not subscribe No email notification Instant email notification Daily email notification Weekly email notification Default Thread Subscription Mode:

From the drop-down list, choose "No E-mail Notification"

Next click "Save Changes"