How can I track the user's email on my site?

Question

PHP

Today a similar situation occurred:
I am looking for tickets online on a third-party site. After a while, I receive a message about discounts on tours in the mail. Coincidence? I don't think.
there were several such situations.
- for example, a week ago I was looking for a service to promote my account on Instagram
and after a while a message comes from Business Youth about the training "Promotion on Instagram".
- I'm looking for sushi in my city, and then I receive a message from other companies about sushi delivery in your city
. I know that you can get the id of the user in VK who visited your site. But how can you get an email?
PS I was not authorized in the mail. VK too.
PSS if you know how to effectively implement this, please indicate the price.
Thank you.

Answer 1

This is implemented using Third Party Cookies: https://www.youtube.com/watch?v=80bRnyBiy_4

Answer 2

Did you enter your email anywhere? Because if you entered your mail in any form, then you can safely send you a letter. Without entering the mail somewhere, they will not be able to send anything to you because they do not know the mail. When registering, you can write mail, when subscribing (if there was one), in any case, you wrote this mail in some field and there is just a script for sending letters to your mail (either successfully registered or news or something else)