Earlier quoted context omitted.
I would not consider it "best practices" to automatically unsubscribe someone who legitimately subscribed. Have a double opt-in, and then assume they're interested until they explicitly unsubscribe. I'm subscribed to some mailinglist that I don't actually read but would be upset if they auto-unsubscribed me, because if I'm ever interested, I want it to be there.
What I described is literally listed under "best practices for bulk senders" by Gmail. These are hoops I'm not fond of jumping through either, obviously, but if Gmail marks all my email as spam I lose 4000 subscribers overnight so I do what big G asks me to do.
It doesn't mention pixels anywhere, though.
It does contain the line:
> "Consider unsubscribing users who don’t read your messages."
But that's only after lots of mention of opt-in and unsubscribe options. And ultimately, you can't really know whether users read your messages or not.