How Image Blocking Works in Email

Have you ever tried to read an email and the images were blocked? What a buzzkill. Why is it even a thing

Chapter 1

Email clients and image blocking

At one time, email clients widely blocked images in emails to protect you from nefarious email senders who might try to use images to compromise the security of your computer or mobile device. It was a widely used tactic among spammers to send image only emails, and email clients used image blocking as a first line of defense in order to protect their users.

Back in 2013, Gmail took a new stance and announced that “images would display across desktop, iOS and Android.” And, instead of serving images directly from their original external host servers, Gmail would instead serve images through Google’s own secure proxy servers. Essentially, this meant that Gmail users would never have to click that annoying  “display images below” link again. Although, if they preferred, they could adjust a setting to ask before displaying external images.

This was a game changer for Gmail users and marketers, as now when emails arrive in Gmail inboxes, the images displayed by default. Oddly enough, though, just a year later, Litmus released stats that revealed that 43% of Gmail users read their emails without having images on.

Every client has its own default settings regarding displaying/blocking images. And while most email clients have a setting to turn images on or off, some offer conditional settings which are contingent upon known senders or other factors.

Litmus created this helpful chart to show which email clients block images, render alt text and render styled alt text.


Chapter 2

How to deal with blocked images

Image blocking doesn’t have to be a big deal as there are some very simple and effective methods to handle it and ensure your subscribers have the best possible experience with your campaigns.

Alt text

One of the easiest things you can do to combat image blocking is to add Alt text to your images. Alt text is simply the text that is displayed by the email client instead of your image when images are blocked. Using alt text is helpful because it can tell your subscriber what the image is in order to give them context and compel him or her to display the images.

By adding alt text, you’ll ensure your subscribers see text that will explain your image instead of just seeing a blank box if their images are turned off by default.

How to add alt text in Campaign Monitor

Our intuitive email builder makes is super simple to add alt text to your images.

When adding an image to your email, simply add your “explainer” text in the field that says alt text as illustrated in the example below:

Use text-align to align your alt text

Setting the line-height in the style for the image to be equal to the height of the image will make sure the alt text is vertically aligned in the middle. Generally, changing the line-height will change the vertical alignment of the styled alt text.


The second way you can combat blocked images is to ask your subscribers to whitelist your emails or add you to their safe senders. You can send these instructions in your welcome email so your subscribers will get your emails from the very start and see all your beautiful images.

Each email client has a different process to whitelisting your emails, so we did the groundwork for you to make it easy. All the instructions are available in this handy guide.

Chapter 3

Wrap up

Blocked images in email can be annoying, but they don’t have to be a big deal. By using these tactics the images in your email campaigns can shine in the inbox.

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