Since i have the entire domain mapped to my account, which means that
[email protected] (*@mydomain.com) will come to me.
So, lets say you're signing up to Top Bucks (for example), you would signup with an email address like
[email protected] and if anything ever comes to that email address, other than what is supposed to (top bucks info) you will know where/how they got your email.
It isnt anything special but atleast you'll be able to tell where the spammer got your address from.
Enjoy!