Do spam filters penalize images?

You've probably heard it: images trigger spam filters. So you start stripping out your product photos and wonder if your emails will ever look good again. Here's the good news. Images themselves don't cause spam filter problems. The real issue is a bit more specific.

Spam filters need text to evaluate what your email is about. When you send an email that's almost entirely images with barely any readable text, filters can't do their job. That pattern also happens to match a classic spammer trick, sending one giant image to dodge content scanning. So the filter gets suspicious. Not because of the image, but because there's nothing else to go on.

A reasonable guideline that deliverability folks often use is the 60/40 rule. Roughly 60% text to 40% images. That's not a magic formula filters enforce exactly, but it reflects the idea that your email should have enough real, readable content for a filter to assess its legitimacy. If your email reads well with images turned off, you're in good shape.

A few things that actually matter alongside this ratio:

• Alt text on every image. When images are blocked (which happens more than you'd think), alt text tells the reader what they're missing. It also gives filters readable content to analyze. Don't leave it blank.
• Avoid image-only emails. An email with one big banner image and a "click here" link at the bottom has almost no text. That's the pattern that gets scrutinized, not your product gallery with good descriptive copy around it.
• Broken image URLs hurt more than the image itself. Hosting images on sketchy domains or using expired URLs is a real red flag. Keep your image hosting clean and consistent.
• Test with images off. Open your email with images disabled and ask yourself if the message still makes sense. If it's confusing or there's no visible call to action, that's a design problem worth fixing.

The takeaway is that visually rich emails can perform just fine. E-commerce brands and product newsletters send image-heavy emails every day without landing in spam. What gets them in trouble is when the design choices reduce readable content to almost nothing, or when their overall sender reputation is already shaky and a thin email tips the balance.

If you want to run a quick check on your subject lines and content before sending, try our free subject line tester. And if you're consistently landing in spam despite doing everything right, the SOS hotline is free and we'll help you find the actual cause.