It's crazy how wrong this is.
> Immediately when an email is received, Google loads the images in it and stores a local copy for when the use wants to read the email
No, they don't.
> in fact, whether or not the Gmail account to which the mail is addressed even exists.
No, they don't, *especially* if the Gmail account doesn't exist. Like every other provider, if an account doesn't exist, they reject the message before any of the data has even been sent.
> Thus, anyone who sends a mail to a Gmail account can count on the tracking image being read - but by the server, not the user.
ergo, this isn't true at all.
The thing that Google _does_ do is to load all images in an email via an image proxy. That obfuscates the IP, user-agent, and other information about the recipient looking at the message. All images are loaded at time of opening though.