What is the count of reading emails based on?

Question

Programming

Now many mailing list systems offer a technology where you can see how many people have opened your letter. Letters in html format of course.
So I think how they think, insert some kind of pixel image into the letter and consider requests for this image on the server?
It hurts to have so many different pictures for all the clients and emails. JS is banned due to security obviously...

Answer 1

A 1x1px transparent image is inserted into the letter. And they try to count on the server how many requests were made to it.
But, already all email clients (both Destkop and web) block the loading of images, js, css, etc.
So you won't get much from it.

Answer 2

Yes, the number of image-counter downloads. Sometimes automatic loading of an image is blocked, which means that viewing will not be counted.