bill - 6:32 am on Dec 13, 2013 (gmt 0)
Gmail blows up e-mail marketing by caching all images on Google servers
Ever wonder why most e-mail clients hide images by default? The reason for the "display images" button is because images in an e-mail must be loaded from a third-party server. For promotional e-mails and spam, usually this server is operated by the entity that sent the e-mail. So when you load these images, you aren't just receiving an image—you're also sending a ton of data about yourself to the e-mail marketer.
Loading images from these promotional e-mails reveals a lot about you. Marketers get a rough idea of your location via your IP address. They can see the HTTP referrer, meaning the URL of the page that requested the image. With the referral data, marketers can see not only what client you are using (desktop app, Web, mobile, etc.) but also what folder you were viewing the e-mail in.
But Google has just announced a move that will shut most of these tactics down: it will cache all images for Gmail users.