Just about every single one of the email newsletters you receive from anyone does this. It's for tracking clicks to links in an email, opens of an email, etc.

Not apologizing for PIA - They definitely shouldn't be doing it if they're trying to advocate for privacy. But just stating it's extremely common practice and the default for most email services. I use it on my e-commerce websites so that I can send specific emails to people who have viewed a certain page, abandoned checkouts, opened a certain email but didn't convert, etc.