How to send HTML emails with a hidden pixel?

Question

Email

Friends, tell me, please! Google doesn't know... Or I'm looking in the wrong way.
I'm new to this, so don't judge too harshly.
In general, I registered on clickmeter and generated a hidden pixel. The task is to insert it into a mailing letter so that it is really hidden. A hidden pixel is a piece of code, it is clear that the letter must be HTML or part of it must be HTML. Google is full of useless information about how to type up HTML templates so that they attract customers, but I don’t need it at all.
My task is to create a letter like "Good afternoon! ... Text ... with respect!". And for this letter to come in the form of plain text, but when it was loaded, I displayed the acc. statistics. And it is desirable that I could write this letter from TheBat! or Postbox (on Mac). These are the clients that are installed.
How to do? Help me out plz :)

Answer 1

First, you need to identify the client. Not all email clients have the function of templating letters.
The pixel is inserted simply as a piece of code. Like a picture. When the recipient opens the email, their mail client goes to the address of the picture, waiting to load that picture, which is the request to the server. Naturally, the server does not return a picture, but simply some kind of response, for example "200", after which the server registers this request in the form of statistics, saying that there was one letter / page opening (depending on what kind of service you have).