Browser Security

Hi,

I was trying out a webpage the other day that allowed anonymous
browsing.

It gave the opportunity for me to see what is sent when not using
anonymous browsing.

When not browsing anaonynously, I noted that my ISP address was sent.
This did not surprise me. But I also noted that my email address
supplied by my ISP was also sent.

My question is: how can Internte Explorer know this address, it is not
stored in the browser, to my knoledge.

Thanks

S