Subscribing to content when not logged in?

Hi All

We've noticed that visitors who view our community while not logged in can still 'subscribe by email' to be alerted to new content in certain applications (such as a blog for instance). However, I can't identify these in the activity reporting area? 

When they subscribe, they're asked for their email address and then sent a verification request to that address. Where is their email address then stored in the community and how is that used? Where can I find out how many 'anonymous' users have subscribed to content? 

We were also wondering whether it's something we would be able to disable/remove from our community as we'd prefer users to have an account in order to get the benefit of being notified of new content etc. 

Any suggestions?

Lisa