Image blocking is when an email client prevents images from loading automatically inside a received message, showing blank spaces or broken image icons until the recipient manually chooses to download them.
Why This Still Happens in 2026
Security is the primary driver behind image blocking email clients still practice today, not bandwidth, despite bandwidth being the more commonly assumed reason. Microsoft has stated directly that blocking images by default protects recipients from potentially malicious code embedded in image files and from viewing offensive content before a sender’s legitimacy is confirmed.
- Outlook desktop clients remain the most consistent practitioner of blocking images by default.
- Most other major clients, Gmail included since 2013, now load images automatically by routing them through a proxy server that scans for malware first, removing the need to block them outright.
The Numbers Are Bigger Than Most Senders Assume
Image blocking statistics have stayed remarkably consistent over the years:
- 43 percent of Gmail users had images turned off, even after Gmail switched to loading images by default (Litmus research).
- 30 to 40 percent is the broader share of email opened with images blocked across all major clients combined.
- Only about 5 percent of users ever bother changing their client’s default image setting.
That means a meaningful share of every list is viewing every campaign as a text skeleton with blank boxes unless the design specifically accounts for it, and this isn’t a problem that resolves itself over time.
How to Design Around Image Blocking
The core defenses are straightforward, but only work if applied consistently across every campaign:
- Write real alt text on every image, treating it as if it needs to carry the message on its own, since for a real share of recipients, it will.
- Keep essential information in live text, not baked into an image, the offer, the CTA, and the core message should all still read clearly with every image stripped out.
- Avoid building a campaign as one large image with no text underneath. This is the worst-case scenario, since a blocked-image version of that email is functionally blank.
- Place the CTA as a styled text button where possible, not an image-based button, so it remains clickable even when images don’t load.
The Metric Distortion Worth Knowing About
Understanding what is image blocking in email doing to your reporting matters as much as designing around it visually. Open rate tracking relies on a small tracking pixel, itself an image, loading when an email is viewed.
A recipient with image blocking enabled who genuinely opens and reads an email won’t register as an open at all, since the tracking pixel never loads.
This means open rate as a metric systematically undercounts real engagement for any list with a meaningful share of image-blocking subscribers, which is one more reason click-through rate and conversion tend to be more trustworthy signals than open rate alone.
Related terms:
Adflipr’s drag-and-drop email builder makes it easy to combine live text with images, so campaigns still communicate clearly even when images don’t load.
