1. All posts in a category.
2. All questions in a category, but not replies (unless you are "watching" that question)
3. Only posts in questions that you are "watching"
4. Nothing.

To enable #1 and #2, go here: Email Notify Subscriptions Subscribe to the categories that you'd like to be subscribed to. For #2, check the "Questions Only" box and submit.

For #3, you are automatically set up to "watch" questions that you have posted to. Additionally, you can click the "watch" link on any question to start watching it.

For #4, edit your profile here: Edit my profile Turn off Reply Notification. You will not receive any of the above e-mails, even if you request them.