Ignore Topic is different from Notify I think.
Given the original question about turning off email notices, I think Ath is right.
More generally, if you go to your profile, in the Notifications and Emails
section, you will find a list of all topics you are subscribed to receive notifications on, and you can disable them there.
(The Mark Thread -> Ignore feature Carol is talking about is to really ignore a topic so you don't even see it listed anymore, at least in the new topics lists).