[giovannibajo1]

FWIW Gmail does that: it triggers trackbacks from a pool of Google-owned IP addresses that don’t map to any specific users, and then serves themselves the images to the clients. This is why they now load images by default: there’s no more privacy issue.

[Sephr]

There is still a privacy issue since Google only caches external images at read-time, leaking the time you read your email to the sender.

[mmirate]

GMail is itself a major privacy issue.

[dingo_bat]

I see a huge problem in this. Mozilla likely won't use IP to identify users. They will use the unique link in each email.