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Yahoo! Mail Introduces Image Caching—What Marketers Must Know

Yahoo! has quietly changed the way it handles images for Yahoo! Mail users. The inbox provider now caches all images and serves them via their own proxy servers, similar to Gmail which introduced image caching in December 2013.

Yahoo!’s introduction of image caching has a significant impact on the level of insights marketers can get from Yahoo! Mail users, and it can even impact the reliability of dynamic content.

Here’s a breakdown of all the facts marketers must know about the recent Yahoo! Mail update.

What’s image caching and why does it matter for email tracking?

Beyond their visual appeal, images serve a very important function in email marketing. Images are used to track email opens and engagement, providing marketers with valuable data about when, where, and how their campaigns are being read.

Email tracking relies on a unique image–often referred to as a tracking pixel—to be included within an email. Every time the image is downloaded from the server, the tracking software marks that as an email open. To count opens reliably, software tools need those images to be downloaded every time someone opens an email.

When an image is cached, it is downloaded from the original server and stored on a proxy server. Subsequent views of the cached image will always load from the proxy server rather than the original server, effectively rerouting all the image downloads along with the associated tracking data that comes with the image download.

How can image caching impact email tracking?

When an email is opened in Yahoo! Mail, image caching limits the detail-level of email insights. While marketers can still see how often an email was opened, we can no longer get detailed insights on…

  • Opening environment
    While previously it was possible to tell a Yahoo! Mail open in the web client apart from an open in the Yahoo! Mail mobile app, with image caching all of these opens look exactly the same. In Litmus Email Analytics, all Yahoo! Mail opens are now reported together as Yahoo! Mail via Yahoo’s Image Cache.
  • Email engagement 
    Yahoo! Mail’s image caching makes it impossible for the tracking pixel to calculate how long a subscriber engaged with your email. In addition, prints and forwards coming from Yahoo! Mail can no longer be tracked.
  • Geolocation 
    It’s no longer possible to know where your subscribers are based when opening your email. All opens will show the location of Yahoo!’s proxy servers that are used to cache the images. For Gmail, the opening location is reported as Mountain View,  (CA), and Yahoo! Mail opens are now showing Sunnyvale (CA) as the opening location. If you see an unexpected increase in email opens in the California area, it’s likely that Yahoo! Mail’s image caching is the cause.

How can image caching impact the use of dynamic content?

The introduction of image caching can impact the reliability of dynamic content for Yahoo! Mail users if you rely on email analytics insights to serve content dynamically.

For example, if you use geolocation insights to personalize email messages—meaning you look at where the image is downloaded and feed users dynamic content based on their location—your dynamic content could effectively break. Instead of being able to see where a reader is located, you will see where Yahoo!’s proxy server is located, resulting in dynamic content tailored to the proxy server’s location.

To avoid serving Yahoo! Mail users inaccurate content, you could segment out subscribers who open in Yahoo! Mail and serve them fallback content that doesn’t rely on geolocation information provided by email tracking data.

The impact of Yahoo! Mail image caching will vary by brand

Yahoo! Mail has lost market share over the past years. Today Yahoo! Mail holds only 2% of the overall email client market share. Depending on your industry and the individual makeup of your subscriber list, your share of Yahoo! Mail subscribers might be higher, and you might see more significant changes in your email analytics data.

If you have a high number of subscribers that use Yahoo! Mail to open your emails, pay close attention to your email analytics data and keep in mind that unexpected changes in your metrics—especially when it comes to looking at engagement tracking, geolocation data, or reading environments—might be caused by the introduction of image caching, not a change of your subscribers’ behavior.

Do your subscribers open in Yahoo! Mail?

Understand what email clients your audience uses to read email, and if they’re impacted by Yahoo! Mail’s image caching with Litmus Email Analytics.

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Bettina Specht

Bettina Specht

Bettina Specht was the Senior Content & Lifecycle Campaigns Manager at Litmus