As someone with a daily email "newsletter" of my own [1], I am aware of (many of) the vagaries of spam filters. I use plain text only, though, so I couldn't use tracking pixels even if I wanted to. I do unsubscribe users if messages start bouncing but I have no way of knowing if they get silently dropped or spamfoldered.
As someone who subscribes to lots of newsletters, the "interact or we will auto-unsubscribe you" thing still annoys me.