[girvo]

Gmail does exactly that, I believe? It proxies the external resources to hide your IP.

What it can’t do sadly is strip out tracking functions (unique IDs and such). Dunno how that could even be solved tbh

[account42]

Gmail proxies the images when you open the email.

What the parent is suggesting is for Gmail to download the images as soon as the server receives the email, thereby rendering any tracking data meaningless.