Dec 6, 2013

How Gmail’s Image Caching Affects Open Tracking

A few days ago, the Gmail folks changed how they display images in their emails. In the past, Gmail would make a request for an image every time an email was opened. But now they temporarily store those images—even the one we use for open tracking.

You may know this already, but along with most ESPs, MailChimp tracks opens by placing a tiny, single-pixel-sized image in each email. When someone views images in the email, our image-hosting servers get a request for the pixel-sized pic, and we use that request to track opens for each subscriber.

Using cached images is a fine idea for Gmail, but it has the potential to mess with open tracking for ESPs. Fortunately, MailChimp can still detect the first request for the open-tracking pixel. This won’t interfere with the count of “unique opens” you get in your reports, but it could prevent us from seeing multiple opens per subscriber.

We’ve done a few quick tests around the office, and, as far as I can see, this won’t affect POP- or IMAP-configured mail clients. The iPhone client appears to count multiple opens, but we don’t know yet about the behavior of the Gmail app for iPhone or Android. Those two are pseudo-web-based, so I can see them being affected—if not now, then in the future.

You’ve got to love Google for shaking things up every now and then. Gmail’s tabbed inbox changed how subscribers opened our emails, and now image caching changes how we track those opens. The good news is that we’re still able to track unique opens for each and every one of your subscribers.

UPDATE 12/12/13

In Gmail’s announcement today, they said image caching allows them to securely turn on images by default. Image caching still lowers our ability to track repeat opens, but turning those images on means we’ll be more accurate when tracking unique opens. At least, theoretically it should work that way.

By leaving images turned off, Gmail has been allowing subscribers to open emails without downloading our tracking pixel, so those opens were invisible to us. If Gmail is going to display images automatically, those previously invisible opens should suddenly become visible.

That’s exciting in a nerdy data way, but keep in mind it doesn’t affect the number of subscribers actually reading your email. It just makes the count of unique opens more accurate. Then again, maybe seeing your beautiful email content will get subscribers to keep opening in the future.