You might know of this solution: in GMail, you can write your email: email@example.com (for example) in the following ways:
… And so on, pretty much any combination of dots and labels.
You might be tempted to use firstname.lastname@example.org for each web site you register with.
The trouble is, the +label solution is pretty much a known fact, and if someone sells a database of emails, including yours, the entity who buys the database with your email in it might automatically remove all the dots and +labels from GMail addresses.
I still think that you should be using +website label to each site you register with, so that you may know if they sell your email, I’m just saying the solution is not bulletproof.