Email analytics and Gmail image caching: the 5 things you need to know

Gmail EmailGoogle stirred up a hornet’s nest recently when it announced that Gmail now cached images within emails. While image caching improves the user experience, the email marketing community scrambled to understand how caching impacts image downloads, which serve as the mechanism for tracking email open activity. After reviewing the responses from several notable email service providers, including Campaign Monitor, Constant Contact, ExactTarget, MailChimp, and Responsys, it appears that the overall change is positive for email marketers.

Here are the 5 things that you need to know:

  1. Images are now displayed by default. In the past, users on desktop and mobile devices didn’t see images in emails unless they clicked on the “Display images below” prompt to activate image downloads. Now images are automatically displayed. While users can disable this feature by visiting the Settings > Images section of Gmail, this streamlined approach now ensures that all most email open activity is now tracked.
  2. Unique opens can still be tracked, even for the same recipient. While some email service providers initially reported problems with tracking opens, others confirmed that unique opens can be counted each and every time an email is opened. According to tests by René Kulka, a German email evangelist, the image cache can be “busted” by serving the header information for each image with a content-length of zero. Hopefully all email service providers will update their code to take advantage of this workaround in the near-term.
  3. User location and device information will be skewed. The tracking image was previously used for transmitting the user’s IP address and device information. Now that all images are cached, the IP address appears as Mountain View, CA (aka, Google home base) and device information is no longer available. Unfortunately, attempts to circumvent this restriction have failed so far.
  4. The rollout of image caching impacts only a small number of users until early 2014. Google indicated that image caching would be initially visible initially to only desktop users, which accounts for 3% of email clients worldwide (according to Litmus). The majority of email clients are on mobile devices, which are not expected to see this change until early 2014.
  5. Click-through rates are not impacted by image downloads. Email marketers measure email campaign success using both opens and click-through metrics. Marketers will likely focus their attention on the latter metric in the future.

And here’s a bonus thing that you need to know if you are an email marketing practitioners:

When you are setting up an email, you’ll need to rename the image file whenever you update the image. I would think that this additional stumbling block will force you to seek an alternate email client platform for testing, such as Hotmail or Yahoo.

In summary, the image caching update is an important win for everyone. Email recipients will see messages the way that marketers intended them to look. And while the loss of device information may make email design a bit more cumbersome, the loss of IP information should ease consumer’s privacy concerns with being continuously tracked.

Do you think Gmail image caching is a good thing or a bad thing?

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