When you give your email address to a website, you hope that they don't sell or trade your address to a bunch of spammers. Well if they do, here is a simple way to see what sites are responsible for what particular piece of email. This requires you have a Gmail account.
If your Gmail login name was [email protected] and you went to samplesite.com to fill out a registration form, instead of just entering [email protected] as your email, enter it as [email protected] instead. When Gmail sees a "+" in an email address, it uses all the characters to the left of the plus sign to know who to send it to. In this example it would still send it to [email protected].
Now whats cool is if you search Gmail for username+samplesitecom, you will see all massages that were sent to that email address.
To see who is responsible for sending a specific message click the Show Details link and you will see the complete address.