I've been on the receiving end of this from one or two online invitation services (Paperless Post, maybe?). Had a friend say "can you come to my party or what?

I've been on the receiving end of this from one or two online invitation services (Paperless Post, maybe?). Had a friend say "can you come to my party or what? You're the only one that still hasn't opened the invitation email". I never had to sign up for an account to imagine what the service was doing - showing "opened" stats straight out of Sendgrid or the like. I had a similar reaction - email open tracking is something you assume, by default, that regular individuals can't do. And I found it very invasive, even though I know the same tracking exists on all the non-personal email I received. Since then I've made it a point not to open those invitations until I know I'm ready to respond - since "I never saw the email" is a less harmful conclusion for my snooping friend to draw than "I opened the email and decided not to respond."