Whether or not you agree with email tracking, the language feels a bit like propaganda:

"YOU'RE PROTECTED. WE BLOCKED A SPY TRACKER IN THIS THREAD"

"A spy tracker" seems a bit dramatic and it's far from a neutral description. What about just:

"This email contained a tracking image allowing the sender to see if you've opened it, we've blocked that for you."

The main use of this feature is to track open rates so that marketers can improve their marketing efforts. Block them if you disagree, but there's no reason to make it sound so nefarious.