That's a very dubious assertion. Formats are in the content of the email. Different formats won't tell you why one email was opened while another was not. Form

That's a very dubious assertion. Formats are in the content of the email. Different formats won't tell you why one email was opened while another was not. Formats can include different titles and descriptions, which can make a huge difference in how often users open your emails. Also just different kinds of emails you might want to send (maybe you send some users an email with a coupon, and some with a new product notification). Maybe you don't see the value in having people know whether you read their email, which is fine, but there are clearly tonnes of legitimate use cases for having that kind of information. If I know a segment of users on my email list never open a particular type of email, it is better to just not send them that kind of email, both for the sender and recipient. Regardless, I think Gmail killed tracking pixels by loading images through their servers anyways.