Gmail hit email marketers with a couple major changes in 2013: Gmail “inbox tabs,” which happened back in late May; and cached image loading, which just happened in December.
So, what happened? Two things really. On the front end, Gmail users now see images displayed in their emails automatically. (Before, they had to click “Display images below” every time they wanted to see an email in its entirety.) On the back end, there’s a bit more happening. Images that are automatically displayed are first cached, then called from Gmail’s servers — not the sender’s servers — when the email is opened.
What this means is that every email will now display images by default (unless the user disables the feature). The tradeoff is that we’ll get less user data, like IP address, geolocation or email client. (We actually get this information, but it reflects Gmail’s server data in Mountain View, California, not the user’s info.) This is intentional, so that Gmail can protect the privacy of its Gmail account holder. There’s one exception: “Opens.”
Emails sent with a unique tracking pixel, like those sent through AimConnect, are tracked to know whether they were opened. Every single email has a unique image URL assigned to it to know if and when it’s opened. And because emails are set to automatically display images, this unique image loads too. Consequently, you’ll get a more accurate read on opens (which will likely be higher than historical open rates).
Technically speaking, neither of these changes affect every Gmail user — only the ones who view their email through webmail (www.gmail.com), the app for iOS, or the app for Android. We estimate this to be roughly three percent of most lists, which is consistent with what other ESPs are reporting.