Image Blocking in HTML Email

Many people, either by email client defaults or personal preference, are blocking images in the HTML-formatted messages they are accepting. And then there are a small number of people who block HTML entirely. According to a study by Merkle in 2009, only 48% of email recipients see images automatically… In any case, it’s logical for recipients to block images and good practice for us to prepare for this scenario.

So what happens to our emails when images are blocked? What are the best practices for ensuring accessibility and optimizing presentation therein? What are default settings across the board? Let’s get down to answering these questions.

The Verdict

Yes!

Proceed with caution. We should be giving serious consideration to image-blocking and what we can do about it. It’s natural and reasonable why people disable them, but with the right approach we can improve the experience for our subscribers.

Default email client settings

Every client has its own default settings regarding displaying/hiding 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. The following table outlines the default settings of popular desktop- and webmail-clients. (Note that We are using the settings of our own versions of each client and that settings may differ from one version to another).

We have included contextually-relevant references to ALT attributes as part of this article. For a more in-depth look at how ALT attributes render in popular email clients, see our ALT attributes research.

Email Client Images displayed by default Images disp. for trusted senders Renders ALT Text
Desktop clients
Outlook 2007 No Yes Info
Outlook 2003 No Yes Yes
Outlook for Mac 2011 No Yes Yes
Outlook Express Yes No Yes
Outlook.com No Yes Yes
Apple Mail Yes No No
Thunderbird No Yes Yes
AOL Desktop No Yes No
Lotus Notes Yes Yes Yes
Webmail clients
Outlook.com No Yes No
Yahoo! Mail Beta No Info Yes
Gmail Yes Yes No
AOL Webmail No Yes Yes
Mobile clients
iPhone/iPad Yes Yes Yes
Android default No No Yes
Android Gmail Yes Info No
Windows Mobile 7 No No No
Blackberry OS6 No No Yes

So now that we’ve covered the settings in popular email clients, let’s outline how we can help our emails survive image blocking.


Recommendations for Successful Deployment

From a designers perspective, an email is successful when it meets the following goals:

  • Retains visual integrity in the most commonly used email clients with images enabled.
  • Retains readability in the most commonly used email clients with images disabled.
  • Is readable to people with visual disabilities and navigable to people with mobility disabilities.
  • Is low in weight for recipients using mobile devices and dial-up connections.
  • Is deployed to a permission-based list of subscribers.
  • Meets CAN-SPAM Act requirements.
  • Legitimately passes common tests employed by spam filters.

Looking at this list it becomes clear just how important it is to consider image blocking when designing/developing an email. Dependency on images can lead to failures on many different levels. Preparing for a scenario in which images are disabled puts us at an advantage to oblige the settings/preferences of a broader range of recipients.

Become a “Known Sender”

Nearly every email client in my test suite enables people to automatically display images when a message is from a “known sender” (senders appearing in white lists, contact lists or address books). Because our subscribers have requested to receive emails from us, they will naturally want to ensure they receive the messages. Spam filters can disrupt legitimate communication when subscribers are unaware of how they function. With a couple, simple notifications we can increase our chances of success:

  1. Ask a subscriber to add the email-list address to their address book (right on the subscribe form) and briefly explain why.
  2. Enable a double opt-in subscription process, and send a plain-text confirmation which includes a request to add the email-list address to a recipient’s address book. And, again, briefly explain why.

Informing a subscriber about this simple step will increase our chances of images being enabled and will help us legitimately pass through spam filters.

Prepare for Disabled Images

So we’ve created a structurally-sound template, we’re preparing to send our email to a permission-based list of subscribers and we’ve taken steps to see our list email-address into the address books of the said subscribers. There are still a number of people on our lists who will intentionally block images, and therefore we should account for that scenario.

I wrote an article outlining a technique for this very purpose. With the releases of Yahoo Mail Beta and Windows Live Mail we lose the ability to integrate the aforementioned technique. However, Ryan Kennedy from the Yahoo Mail team has pointed out that they are looking into potential resolutions for this obstacle.

Positioning aside, there are some things we can do to retain the integrity of our emails when images are disabled:

  1. Begin an email with HTML text or logical ALT text. We can decide what a reader sees in a preview pane or small message-window. If we’re prepared, we can optimize the experience of scanning messages. Moreover, some applications offer the ability to preview the first few lines of text before an email is loaded/viewed.
  2. Use ALT attributes. This seems so obvious, but we don’t have enough fingers and toes to count the email newsletters we see without them, so there it is.
  3. Use captions for contextually-important images. In lieu of proper support for ALT attributes across the board, we can add captions to images which are vitally important to the content of an email.

Avoid Image-Based Emails

Again, this is something which should seem obvious. But image-based emails are often practiced as a simple, easy method of delivering a pretty design irrespective of the rendering circus among the array of common email-clients. When we ponder image blocking as part of the rendering equation, it’s easy to see how an image-based email could be completely destroyed with a single preference. Furthermore, this doesn’t take into consideration file sizes for mobile/dial-up recipients, accessibility for those visually impaired or the HTML-to-text ratio that popular spam filters apply with their algorithms.

In summary, we should be giving serious consideration to image-blocking and what we can do about it. It’s natural and reasonable why people disable them, but with the right approach we can improve the experience for our subscribers.

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