What Happened: At some point on or around the 2nd of December 2014, for emails received by Gmail users, Google has started routing requests for images via its own [proxy] servers and subsequently caching them. After externally hosted images within an email have been downloaded by the user for the first time, subsequent requests for these images (when the user reopens the email) are then fulfilled by Google’s own content delivery network (CDN). Google is showing images in all emails by default, where previously user authorisation to download images would be required.

How: Google routes all user requests for images via it’s own [proxy] servers. After the first download, Google stores a copy of [caches] the images. Image URLs which were present in the HTML sent to the user, such as website.com/image.jpg are then replaced with Google’s own rewriten URLs, such as googleusercontent.com/ image.jpg. The end result from the users point of view is no different.

Why:According to the official Gmail blog, the primary reasons are user experience and privacy. If Google is serving images via their own CDN, they can be delivered faster and more reliably from the point at which they have been acquired from the sender. Overall load times from the users point of view should subsequently improve. Additionally, as Google is now routing image requests via proxy servers, the user’s location and device information are now masked from the sender. It is unclear whether Google itself is gathering this information.

Scope: At this stage, users of the Gmail webmail client are affected. Gmail expects to update mobile apps in early 2014.

Challenges for marketers

Open Rates:

Email opens are tracked using images. Generally speaking, your email service provider (ESP) will add a tiny (1 pixel) image to each email that is sent to a subscriber. Most modern ESPs generate a different URL for this image for each subscriber. By doing this, it is possible to count unique opens, as each request for the tracking image is to a unique URL and can only have come from the single subscriber in question. As such, this does not present a problem for the first open of an email. Subsequent opens however, will result in the user being served a cached version of the tracking image by Google. In simple terms this means you will be only able to track the first (unique) open. Further opens of the same message by the same subscriber(s) can no longer be counted, as no further requests for the tracking image will be made.

The result of this is that overall open rates of emails sent to Gmail addresses are likely to decrease dramatically, as multiple opens are no longer visible. Unique open rates should remain constant. Obviously, this does not mean that emails are not being opened; simply that you do not have visibility of anything past the first open.

Dynamic Images:Serving image content based on location is no longer possible, as Google is routing all image requests via their proxy servers. Subsequently, any software you are using will see Google’s IP address (as opposed to the IP address of the user) and report that the request originated in Mountain View, California (USA). Serving image content based on time (or other factors such as weather) will also be problematic: Only the first open will receive a correct image - from that point forward, re-opens will get the original image served from Google’s CDN - if the time (or other factor) has changed, that will not be reflected, as no request for a new image is made.

What marketers can do

Workarounds:

If you use non-user-specific tracking to count opens - i.e. your ESP does not differentiate between unique opens and total opens by generating a unique URL for each message, you may find that your open rate drops substantially. We advise you contact your ESP in this case. Generally, these changes have taken the ESPs by surprise as much as anyone. When looking deeper into the technicalities of exactly what Google have done, certain ESPs are finding possible workarounds beginning to present themselves.

René Kulka, who blogs at www.emailmarketingtips.de has found that HTTP headers (which are used to provide supplementary information when requesting and sending files using HTTP) can be modified to cause Google not to cache an image. René’s tests indicate that if the “Content Length” header for the tracking image is set with a value of 0 (or not included), Google does not cache the tracking image, which seems to solve the problem. ESPs who do not already employ this method may be working to implement it now.

Summary: As of 11/12/2013, some ESPs, including Lyris, SmartFocus, Campaign Monitor, ExactTarget and SpinnakerPro are reporting that their tracking of open rates from Gmail recipients are unaffected, so the above may offer some explanation. It must be noted however, that Google may alter their caching methods to invalidate such workarounds at any time. In simple terms, the future is uncertain - marketers will have to embrace changes made by Google or other email providers and evolve.