One thing that occurs to me is that I am not certain which version of D.C. you are using. I use Version 1.
To remove your previous subscriptions, go back to the navigation sidebar in User CP and scroll to and click List Subscriptions. This will take you all the threads you are subscribed to.
Look all the way to the right and you will an empty box beside each subscription. If you look and the top (in the header bar), you will see an empty box there as well. If you want to cancel all the subscriptions, click that box. Otherwise you can select threads individually that you want removed.
You will need to do this for every page of subscriptions that appear at top top left where it says Page 1 - whatever.
Scroll to the bottom and look for a drop down menu that says Selected threads:Move to Folder.
In that drop down menu under Update Subscription Type, select No e mail Notification and click GO.
That should do it.