Some email clients perform operations when reading an email which give away information about the reader, to the sender of the message. If you enter your email address into the form on my home page, this web app will send you a confirmation email to make sure you own the email address. In that email there will be another link. Click that link and you will be taken to a page where you can trigger test emails to be sent to you. Those test emails are specially crafted to use a variety of techniques, to attempt to send information back to this server when read. It will then display the results for you.

Test your email: https://www.emailprivacytester.com/