How can I track the opening of emails without services?

Question

Email

Hello.
How can I track the opening of emails?
Sending is conducted stupidly through SMTP.
I imagine it something like this:
Some link is registered, then redirection occurs.
How to implement it correctly, and is it possible?

Answer 1

Usually, an external image is simply embedded with a unique url for each letter. Will work if the mail client / service opens external images.

Answer 2

Can. But unreliable. Because any interaction is under the control of the client. Yes, a teapot, especially one reading with Outlook, will honestly send a read message, honestly open the embedded link. Others are simply ignored. TB, for example, by default blocks all pictures in the mail and does not send responses to "read receipt" requests. Well, in corporate mail, in general, you can do anything - up to cutting out links when delivering letters, as Lotus Notes does.