Your email client sent three emails, with different "hidden image file" urls.
The cheesiest version just makes the image url be something like:
https://example.com/trackingpixel.png?email=dhbanes%40exampl...
and rewrites that query parameter for each of the To: Cc: and Bcc: addresses.
A real implementation will more likely use a UUID instead of just plonking the email address in there, and store that uuid -> email mapping sevrerside.
Each one gets a different image in the email, when they open the email it fetches the image, so the tracking service knows they opened the email.
The image is usually a 1px by 1px transparent png at the end of the email
Your email client sent three emails, with different "hidden image file" urls.
The cheesiest version just makes the image url be something like:
https://example.com/trackingpixel.png?email=dhbanes%40exampl...
and rewrites that query parameter for each of the To: Cc: and Bcc: addresses.
A real implementation will more likely use a UUID instead of just plonking the email address in there, and store that uuid -> email mapping sevrerside.