Any idea what this is about? I doubt Proton has that many trackers, so I was thinking maybe the individual emails? But those would just be triggering when I click on links, which I thought Proton stripped anyways, and I wouldn’t think /e/os would attribute those to Proton either.
Also worth noting that Proton opens any images or other elements server-side, so senders can only “track” Proton servers.