Google’s New Image Caching: 5 Things You Need to Know


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Google has made a new change to how they display images in Gmail. According to Google, for security reasons, now instead of loading an image from an external host server each time an email is opened, Gmail is now storing these images locally on their own proxy servers.

For context, at SendGrid, we perform image tracking by embedding a unique link to a small image file in each email that is sent. When a recipient opens a message and the mail client retrieves this image from our mail server, our statistics engine registers an “open event” for this recipient and records associated information like IP address and browser user agent type. Now that Google is caching their images, this insight is affected.

Google_images

So while this change makes for a more seamless user experience, what will it mean for senders who rely on open tracking? How will your insight into your subscriber behavior be affected?

At a high level, we see this as a “good news/bad news” situation.

“Good” news: Safe images will now be displayed by default, so opens will rise, which will help senders identify more of their engaged users (which is always a good thing!).

“Bad” news: Browser, device type, IP address, and associated geolocation information will be incorrect for some recipients. Re-open counts will also be inaccurate for some recipients.

Let’s take a deeper dive into all of these effects. Below, we’ve identified 5 key takeaways that we’ve observed so far from this change.

But first, please note that this change doesn’t affect open tracking metrics for anyone retrieving mail from Gmail using an IMAP or POP client (Apple Mail, Outlook, Thunderbird, etc.) so subsequent opens will still be tracked through these clients. Just Gmail’s web clients–desktop and mobile (Gmail apps for iOS and Android) are affected.

5 Takeaways

1)   Fundamentally, open tracking still works. SendGrid tracks unique opens, (the first time a recipient opens your email) so this tracking will remain unchanged. What will be affected is tracking on any re-opens you receive on an email (since the image within the email has already been cached). However, multiple opens will continue to be tracked on iOS Mail (if you have a Gmail account set up there). The Gmail apps for both iOS and Android will only track the first, unique open. So, bottom line: if you’re using a different mail client, that’s receiving mail through POP or IMAP, you shouldn’t get affected by this change.

2)    Non-Unique opens will go down.  Since only unique opens will be tracked for Gmail’s web clients, the total number of opens including re-opens will decrease. Since Google is SendGrid’s  #1 recipient of emails, we can also expect that our cumulative open rates for our overall system will decrease. (We are currently running tests around Gmail’s cache to see if we can register more than just unique opens.)

3)    Unique open rates for Google should increase significantly. Google’s new change automatically displays images on desktop, iOS, and Android. Since Android devices didn’t previously download images and all browser-based clients will automatically download images by default, we expect to see a nice increase here.

4)    The gap between unique and total opens will shrink. Currently, there is a system-wide gap between these two metrics. This gap will close due to the decrease in total opens and the increase in unique opens.

5)    Geo stats, IP address, and browser and device type metrics will be incorrect for some recipients. Now that Google is proxying images, senders will  see the Gmail caches’ IP address rather than the recipient’s IP address and will thus have less insight into where the actual recipient is opening the image, since it will only show where the proxy servers are. The same applies for browser type.

Tracking Engagement

While you adapt to these changes, it’s important to remember that SendGrid’s click tracking is also available, and can give you invaluable insight into subscriber engagement. Providing valuable, wanted content that your subscribers want to engage with will help you recapture some of the information (IP address, geolocation, browser and device type) that is lost due to Google’s new image caching. Engagement is truly the bread and butter of email, so sending quality content that invites an action is key.

Bottom Line

While Google’s new image caching may change how we look at some of the statistics we’ve relied on in the past, (multiple opens, geo stats, IP address, browser and device type) it doesn’t affect insight into unique opens or evaluating user engagement through click tracking. We should expect change in our industry. It’s normal and inevitable, so we’ll do our best to adapt and to communicate about it as best as we can. We’ll continue to look into Gmail image cache’s TTL settings, whether this change affects MAPI clients, and how our customers are seeing an impact.

In the meantime, please share your questions and experiences in the comments below.


As SendGrid's Senior Manager of Content, Jillian is responsible for ensuring that SendGrid provides valuable thought leadership content through the blog, whitepapers, webcasts, case studies, and more. An editor and writer by trade, Jillian considers The Chicago Manual of Style one of her favorite reads.

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