>Emails demanding deletion of the memo contained “pixel trackers” that notified human resource managers when their messages had been read, recipients determined. This seems like the worst part (not that the rest is not bad), anyone has an idea of what this "pixel trackers" are and how they actually work?
It's a small transparent pixel loaded from a website (assuming the email client loads HTML). I'd make a unique image called mywebsite.com/jaclaz_read.png and when that image was loaded I'd know you read my email.
I am particularly "old style", I know, but I tend to use not whenever possible email clients that load the html, so an old habit turns out to be also (at least partially) "safer".