Gmail and similar providers proxy all image URLs they receive at the time they receive the email, so you can't tell when a user later opens the email. That said there might be bugs to make your images un-cacheable such that Gmail still loads them later, directly or indirectly, when you open an email.
Compare this with Apple Mail which proxies emails from a different, presumably non-Google IP address and which does so only when an email is downloaded in the background. So while you can't track IP address, yes, and you never could set cookies that I'm aware of without clicking a link first, this means you can still track "downloads" of your email to a local client, just not "opens" - and if your Mail app already downloaded images when the email was downloaded, then it's possible it won't even change that - you might not have been tracking opens this whole time... maybe.
>Gmail and similar providers proxy all image URLs they receive at the time they receive the email, so you can't tell when a user later opens the email.
I searched around and found some articles that makes the same claim[1], but in my own testing that doesn't seem to be the case (ie. I had to click on the email before image would start loading).
I did the same test (although some years ago) and gmail didn't request the images until the email was opened.
Caching the images lazily also means that Google can save a ton in network bandwidth / storage for all those emails that are never opened (which is probably most emails the handle)
This is not correct. They load the URLs at the moment you open the e-mail. You are still trackable. It's just that they open it on backend, so they don't get your IP, but they still know that you opened it.
Compare this with Apple Mail which proxies emails from a different, presumably non-Google IP address and which does so only when an email is downloaded in the background. So while you can't track IP address, yes, and you never could set cookies that I'm aware of without clicking a link first, this means you can still track "downloads" of your email to a local client, just not "opens" - and if your Mail app already downloaded images when the email was downloaded, then it's possible it won't even change that - you might not have been tracking opens this whole time... maybe.