No browser disables JavaScript by default, and disabling it is never a first-class feature: you have to manually figure out when it’s broken things and decide what to do with it.
Meanwhile, there are comparatively major webmail and desktop clients that disable remote image loading by default (e.g. Fastmail’s webmail and I think Thunderbird on the desktop), and all significant clients at least support disabling loading remote images. And in such cases, if any remote image is blocked, the client will put a “remote images blocked” banner with a button to load remote images. This is a first-class feature of email clients.
My impression is that Gmail prefetches ALL email images, and then serves them to the reader via their CDN. (Checking a random email in my inbox demonstrates this, https://ci3.googleusercontent.com/proxy/...)
As a result, I thought there was no signal for tracking pixels? I might be wrong though
They only know when google fetches the image, which can be any time between you receiving it and opening it. I highly doubt it's on the fly right when you open it.
All Gmail does is proxy the request to hide your IP from the server hosting the image file. Gmail does not change the timing of the request, the URL, or the image file.
Yeah. Something I did not expect when I became a mail administrator was meeting a lot of people who actually read those marketing newsletters I spend so much time trying to avoid.
I've got a constant contact sender (a local chamber of commerce) in my tickets right now who sends exclusively pictures of text.
It's common for browser-based email services (such as Gmail) to default to loading remote images.