Open Season: Like Apple, Gmail Is Pre-Fetching Images, Inflating Open Rates

Apple has received most of the attention for its false opens -- the result of pre-fetching and the privacy regime it instituted last September.

But Gmail is also prefetching, leading to marginally inflated email opens, according to Update on the Gmail Web App Prefetching Images, an analysis by SparkPost.

This situation further reduces the efficacy of opens as an email metric. Apple generates roughly 45% of email opens, and Gmail an estimated 30%. But the vast majority of Gmail sends are not being pre-fetched.

One recent study by Litmus found that Gmail has an 89.6% share of webmail opens, and that webmail accounts for 35.6% of email opens.  

Of over 9.8 billion Gmail recipient open events in December 2021, false opens accounted for between 1%-6% of all opens, SparkPost reports.  

“In investigating billions of open events, we can confidently say that these opens are false opens and do not indicate an actual user open event,” Chris Adams writes on the SparkPost Blog.  



Brands can expect their open rates to be inflated by up to 2%. For instance, a company with a 20% open rate in Gmail would in reality be closer to 18%.

Adams says Gmail prefetching occurs when (and we quote):

- A Gmail recipient is ' logged into and has an active session open to the Gmail app (either web or mobile app).'

- An email is sent to this Gmail recipient during an active/open web session.

- Gmail prefetches all images immediately before the web UI displays the email.

- This image prefetch is 'in addition to (and different from) Google Image Cache opens, which occurs when the user opens the email.'

To get technical about it, the image prefetch occurs when the user is logged into the Gmail web application, comes from a Google IP address, and is requested using the following user-agent string: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/42.0.2311.135 Safari/537.36 Edge/12.246 Mozilla/5.0

Note: these open events are different from user-initiated open events triggered by Google Image Cache, Adams explains.

Unlike with Apple, people do not have to log in to a privacy scheme for images to be pre-fetched--"it just happens," Adams reports. 

The takeaway: “As is the case with Apple’s Mail Privacy Protection, senders should treat all open events with care,” Adams concludes. “Opens are just one, and often not the best one, of the many engagement metrics that senders should be monitoring and including when making determinations about user engagement.” 

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