[minsc__and__boo]

Gmail caches by default.

The catch is that Gmail caches all the same images from the same servers, so email marketers get around it by serving tracking pixels with obscure, unique URLs per individual.

Geotargeting fails because it loads on GMail servers.

[Mulpze15]

Yes, I understand the caching part. If Gmail proactively loads/cache the unique pixel before users open the email, then the email reporting is garbage. If they wait for the person to open the email, it is very interesting (even if repeat are not tracked).