About the Email Privacy Tester
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.
The results are dynamic, so initially they will say that none of the tests have succeeded. Open the message in your email client and a bunch of tests might be triggered. Then click the "Load remote images" button (or equivalent) in your client and more tests may be triggered.
If merely reading the message without selecting to load remote images triggers any of the tests, then either your email client has a "privacy bug," or it is not configured for optimal privacy.
I run email systems for a living so hate spam more than most people. I take your privacy extremely seriously. Please check out my privacy page if you want to know more.
The full source code for this application is available at https://gitlab.com/mikecardwell/ept3
Thank you to Adrián Losada for contributing a Spanish translation of this website.