Email standard lets you use a random string in the adress if you type + after your "name".. For examble you have adress hehe.haha@gmail.com, and now you can give dropbox hehe.haha+dropbox@gmail.com and still get the mails that dropbox sends to the same hehe.haha@gmail.com box while "send to" still remains hehe.haha+dropbox@gmail.com.
This is the best way (that I know) to find out where your adress was leaked.
This is the best way (that I know) to find out where your adress was leaked.