I was disappointed to see the Gmail app on the Pixel actually automatically loads images for emails in the spam folder, with no way to turn them off except to turn off image loading across the board.
Gmail already proxies images in emails to their own servers.
But they still only request them when the client views them and not beforehand, so the view tracking still works and even has the proper timestamp for that.
That still tells the spammer you opened the email. I also doubt they do so for third party email accounts, which can also be used in the gmail app.
I mean, don't open the messages in the spam folder?
Suprisingly legit emails sometimes still go to spam. I recently had an actual message from Google go into spam and I didn't put it there.
The problem is that most clients are configured to allow it. So people send email that loads external resources. Now you need a degraded experience for privacy.
If most clients disabled remote resources then senders would include them in the message.
I don't know if I've used a client that doesn't let you turn this off.