„There??s a very simple and cool trick in Gmail to find out if any websites gave your email address away. In this example your Gmail addy is [email protected] (I have no idea why I chose that).
When filling in a registration form whateversite.com [whateversite.com] enter your email address as [email protected]. When Gmail sees a ??oe+” 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].
The additional bonus is that when you search [email protected] in Gmail, you will see all emails that were sent to that address. Then simply click on the ??details?? link to see who sent you message.“
Snippet: Find out who gave away your Gmail address