Gmail Data Analysis Reveals Image Blocking Affects 43% of Emails

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In December, Google announced that images in emails will now show automatically. We’ve kept a close eye on the increased open counts in Gmail—automatic image downloads have given us a unique opportunity to examine the impact that image blocking has had on email marketing for years. What we’ve learned is fascinating, and unveils a critical metric unknown to email designers before now.

43% of Gmail users read email without turning images on.

By comparing open rates before and after Gmail’s switch to automatic image downloads, we can tell how many people view emails without displaying images. When Gmail still blocked image downloads, 57% of Gmail users turned images on.

What about other email clients that block images?

While Gmail isn’t blocking images any more, many email clients still do. If we look at the difference between people reading with images off vs. images on, we can extrapolate that difference to other email clients that block images. Clients that block images would see about a 26% increase in opens, while those that download images would see a 4% decrease.

Email Client

April %

Adjusted %


















Apple Mail















Windows Live Mail




Windows Mail




Show your work

If math is your thing, Matt Brindley (Litmus co-founder and CTO) reveals the data behind the analysis.

Defensive design for image blocking

You can use a Litmus account to preview how your email looks in email clients that still block images. After taking stock of how your emails look with images disabled, consider using “defensive design” techniques to combat the effects of image blocking:

  • Using clear and appropriate ALT text on images. Ensure your email is readable and gets the point across, even without images.
  • Don’t put key copy in images—nearly half of your readers will not see it!
  • Consider styling your ALT text. This gives you an opportunity to grab your reader’s attention, even if images are disabled.

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  • Brad Reeves

    Great article, thanks. if you dont mind, help me understand the math and the assumptions that are applicable here. Reading through Matt’s data analysis, it appears that the “43%” of users that read Gmail with the images off is simply derived using open rates from before and after automatic image downloads where implemented by the Gmail web client. After automatic image downloads were implemented, Litmus can detect “all” Gmail opens, and before automatic image downloads Litmus could only detect Gmail opens where the user had elected to turn images “on”. The difference in the open rates – assuming everything else is equal – is assumed to be the opens that Litmus could not previous detect when images where turned “off”. Ok, I think I got that.

    However, I am not following how you got the 26% increase and 4% decrease in open rates for other email clients. How does that follow? I understand why email clients that block images would see an increase in open rates if we account for those recipients that are opening emails without allowing images (although I dont understand how you arrive at 26%). I dont understand why email clients that show images by default would have their opens adjusted – and in particular, why they would be adjusted negatively.


    • Narong Saron

      Because the numbers have to add to 100%. If you increase in a particular area, another area will drop. This doesn’t mean that the usage has dropped, it’s just the measurable opens does not account for as large of a percentage as before. Since there are now more numbers to count for email opens, clients that did not get a sudden boost in open rates will, get a drop in percentage.

    • Justine, Litmus

      I’ll admit the math is a bit hard to follow—it took a lot of time in Excel to wrap my brain around it, too!

      You’re correct, the 43% number comes from comparing open rates from before and after Gmail started downloading images automatically.

      To calculate the impact of image blocking to the other email clients (and arrive at the 26% increase / 4% decrease), we calculated the percentage increase that Gmail opens saw as a result of image blocking (it was in the ballpark of 132%), and applied this to the other clients that block images by default. If the clients that block images automatically are under-reported, then the ones that enable images automatically are over-reported. However, when you increase 6 of the client’s share by 132%, you end up with a total more than 100%.

      The end result is that you need to adjust the entire top ten to add up to 100%. Increases in one (or six) clients mean that other clients will decrease. This doesn’t mean that the usage has dropped, it’s just the measurable opens does not account for as large of a percentage as before.

      • Danielle Jamil

        Just want to make sure that I’m understanding this correctly. This is ALL based on the assumption that image downloading behavior is the same across email clients. IMO, it is far more likely that users are not downloading images at the same rate as gmail in other clients (different UX, etc.) than it is that the Apple clients are all over-reporting opens. (How would that even be possible?)

        • Justine, Litmus

          Danielle, I agree that UX and other factors may mean that image download rates for other clients that block images may be different. It’s hard to say what the impact may be in clients like Outlook (rather than the single link to download images in Gmail, Outlook puts a message on each individual image). Gmail’s reversal of image blocking gave us a unique opportunity to better understand how often it actually does happen.

          Since Apple Mail automatically downloads images, you can make the argument that open rates there are more accurate. However, when examined next to clients that disable images, they are comparatively over-reported.

  • Dan Hare

    Back in December, you guys also reported on mobile topping 50% for the first time. Since then, I’ve noticed Gmail climb from 6% to 12% and Android drop from 12% to 5%. Is this related to Gmail’s image handling or something to do with user agent strings?

    • Justine, Litmus

      Yes! Gmail image caching has affected how the user agent strings are reported back to us. It’s a bit complicated, but in a nutshell—Gmail Android app opens used to be reported as mobile opens, but now they are reported as webmail opens. Image caching results in ALL Gmail opens looking the same—including Gmail Android app opens.

      See this article for a full explanation:

  • paul

    This is such an important metric I’d really like to know if anyone has done a recent survey across demographics and different email clients to see who is typically reading with images on or off? I’m just a little wary of metrics that have to base partially on extrapolations or assumptions. Google itself claims that only 1% of its gmail users have images off but, I don’t think that’s any more than conjecture either.

    • Justine, Litmus

      I realize it’s a bit of a stretch to assume that other email clients follow Gmail’s trend, but reliable data regarding image blocking is unavailable. Even survey data can be unreliable—self-reported user behavior doesn’t always correlate to actual behaviors :)

  • Jordie van Rijn

    Can the current stats (or derrived stat) give an indication of which percentage of people are experiencing mobile with images off, versus non-mobile with images off (either as percentage of emails, or people)?

    • Justine, Litmus

      Tough call, Jordie. The adjusted figures I ran ran with the theory that image blocking affects ALL email clients equally—that 43% experience with images off, and 57% experience with images on. In practice, that theory might not hold up due to demographic and UI/UX factors. The “view images” links on Android are pretty small!

  • Bill Kirtley

    Am I reading correctly you assume *all* gmail users suddenly started loading images when the default changed? Are you concluding that *no* (or an insignificant fraction) gmail users turn off image loading?

    Can we draw the same conclusion about other mail clients? (e.g., iOS Mail users all do image loading) And therefore are accurately reported in open rate calculations?

    • Justine, Litmus

      For the basis of this analysis, yes, we did assume that all Gmail users left the new default in place. While a bit old now, Campaign Monitor quoted an study from Jared Spool stating that less than 5% of users change their default settings:

      Based on anecdotal and observational data, I do agree that you can draw the same conclusion across other email clients. The option to turn off iOS automatic image downloads for email is quite buried.

      Unless you have data that suggests otherwise—a particularly tech-savvy audience, or users with restrictive data plans—I would wager that most users leave default settings in place.

  • David Vielhuber

    Awesome information – I didn’t know that so much people are not seeing images in e-mails. Definitly will keep this in mind for future projects!

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