email tracking. What options?

Question

contextual advertising

At first, I imagined the work of email tracking similar to the work of call tracking, when only a few numbers are distributed depending on the visitors on the site and the numbers can be, for example, 5-10, and there are 100 ads in contextual advertising and much more. Plus, in the case of call tracking, you will have to pay for the services of a third-party service.

But then I thought that in the case of an email tracker, as far as I understand, nothing prevents showing a unique email address for each ad and not even involving any third-party services - just write a script on the site so that it receives the utm label of the ad number, creates a cookie and demonstrates email corresponding to this ad number. And in the hosting settings, make sure that incoming messages to any, even non-existent email address, are redirected to the main mail with an indication of the address from which the redirect was made. Thus, it will be clear which advertisement is associated with a particular letter.

This is how I see it in theory, but in practice this is how it is done, or have I not taken into account something? For example, it is impossible (or possible) to set up a direct to send a label with the ad number, or what else needs to be taken into account? Maybe an algorithm for transferring information to Yandex Metrica? Didn't forget anything?