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.
Empowering you to choose a better internet where privacy is the default. Protect yourself online with Proton Mail, Proton VPN, Proton Calendar, Proton Drive. Proton Pass and SimpleLogin.
Proton Mail is the world's largest secure email provider. Swiss, end-to-end encrypted, private, and free.
Proton VPN is the world’s only open-source, publicly audited, unlimited and free VPN. Swiss-based, no-ads, and no-logs.
Proton Calendar is the world's first end-to-end encrypted calendar that allows you to keep your life private.
Proton Drive is a free end-to-end encrypted cloud storage that allows you to securely backup and share your files. It's open source, publicly audited, and Swiss-based.
Proton Pass Proton Pass is a free and open-source password manager which brings a higher level of security with rigorous end-to-end encryption of all data (including usernames, URLs, notes, and more) and email alias support.
SimpleLogin lets you send and receive emails anonymously via easily-generated unique email aliases.
I dont have an answer but perhaps relevant context: google analytics is by far the most used solution by marketeers, a lot of newsletters have code embedded so the sender can see if it the email is opened and if so what links are clicked. Opening an email is enough to pull the tracker though, since that is the action that makes the code start running. I would say it is much more likely the trackers are from the emails, but since i'm not a developers I don't know how much analytic software like this is used by them. Also I don't know how effective proton is at stripping them. You could consider using a forwarding service, but that can be a hassle too. I use addy.io, and also have good experience with duckduckgo's service. If you have a paid plan from proton i believe they offer this service too, but maybe it isn't more effective at blocking trackers than what you have now. They did acquire or merged with SimpleLogin, but don't know how much of their service is already implemented in the regular email service.
Ah yeah I completely forgot about "magic pixels" and image based trackers. I was just considering special links. That make sense. Still I do recall hearing Proton saying they block those things, but maybe /e/os doesn't realise they are being blocked somehow.