"This stressed out a lot of email marketers, who quite rightly realised that the new regulations would have a significant effect on their ability to acquire and market to customers via their email address" "The overwhelming majority of commercial email sent today contains tracking pixels and tracking links, these are used to uniquely identify individuals so that opens and clicks can be correctly attributed to them" G…
If they send you an email it means that they obviously have your email address, which I believe is considered personal data. Now, what additional personal data are collected by tracking pixels? > these are used to uniquely identify individuals I would say that this isn't the case. It is to check that the email was read.
You are correct that the email was already personal data. But, GDPR requires that each new use of data be transparently communicated and legally justified (which may or may not mean consent), even if it's only using data you already have. The fact that they have already identified the user does not resolve the issue--GDPR still cares when you collect more data about a known user.
Meaning, even though you are justified using the email address to send the newsletter, you may not be in the clear building an engagement profile associated with that email. Which, apparently, some email marketers do.