Image blocking
Image blocking is the default behaviour of many email clients that prevents images in emails from loading automatically, displaying blank spaces or ALT text in their place until the recipient manually chooses to enable image display. Email clients block images primarily as a security measure: loading an image from a remote server confirms to the sender that the email has been opened (via the tracking pixel) and can expose the recipient’s IP address and device information. Corporate email environments often enforce image blocking as an IT policy.
Image blocking has significant implications for email design. An email that relies entirely on images to convey its message becomes effectively unreadable for recipients with image blocking enabled. Headers that are pure images with no ALT text are invisible. A call-to-action button that is an image rather than HTML text disappears entirely. The proportion of recipients who open emails with images blocked varies by audience and email client, but can be substantial in corporate B2B environments where Outlook with enforced IT policies is the norm.
For B2B email marketers, designing for image blocking is standard practice. This means using descriptive ALT text for every image so the content is still communicated when images are not loaded, using HTML text for all essential information rather than relying on image text, using HTML buttons rather than image-based calls to action, and testing every email with images disabled before it goes out. An email that works without images is not a compromise; it is simply a well-built email.
What percentage of email recipients have image blocking enabled?
Estimates vary considerably by audience and email client. In consumer environments, image blocking is less common as clients like Gmail and Apple Mail show images by default. In corporate B2B environments, particularly those using Outlook with IT-enforced policies, image blocking can affect a significant proportion of recipients. Rather than relying on a specific percentage, the practical approach is to design every email so it communicates its core message and call to action without images, treating image display as an enhancement rather than a requirement.
How does ALT text help with image blocking?
ALT text is a written description added to the HTML img tag that appears in place of the image when it cannot be displayed. When image blocking is enabled, recipients see the ALT text instead of the image, giving them context about what the image shows and, for functional images like buttons, what action they should take. Writing descriptive, meaningful ALT text for every image ensures your email continues to communicate effectively even when the visuals are not shown.
How do I test my email with image blocking?
Most email testing tools, including Litmus and Email on Acid, allow you to preview your email with images disabled as part of their rendering test suite. You can also disable images manually in your email client settings to preview how your email looks without them. Testing both the image-enabled and image-disabled versions of every email before sending is a standard part of quality assurance for any B2B email programme.