How do you know if an email has been read?

Question

gmail

There is a task to keep statistics on sent letters, which should contain the number of viewed letters (opened). This is possible because gmail for business accounts has read receipts, or e-mail marketing sites like woodpecker have read receipts.
The question is how to implement it?
There was an advice like this:
Generate a random small picture and attach it to the letter, if it was uploaded, then the letter was looked at. But this is not very good, because by default, deleted pictures are often not loaded, and if the picture is small, it may be suspicious for antiviruses (because it is not safe, many vulnerabilities work through pictures), and no one wants to be blacklisted .
How does the same gmail do it?
How does woodpecker do it?
How can this be done safely, consistently and accurately?

Answer 1

Yes, only one way - with a picture, as far as I know. unstable and hack. no other way.

Answer 2

The second way, you can generate a letter with a request for reading, the one to whom it was sent will receive a message that you have made such a request. But the user can ignore.

Answer 3

In general, no way. All of these read confirmations are undocumented stuff. Not all servers support them and there is no single standard. A hundred times confirmation will come, but on the 101st it may not come.

Answer 4

But where do you come from, who do not know how to use the search!
Tyts