What design variables impact performance (e.g., layout, colors, fonts)?

Every email designer has a theory about what moves the needle. More whitespace. Bigger buttons. Bolder colors. But most of those theories are never actually tested. Here's what the evidence points to, and how to think about each variable.

Buttons come first. Your call-to-action button is the single highest-leverage design element. Size, contrast, placement, and copy all affect whether someone clicks. A button that blends into the background gets ignored. One that stands out, sits above the fold on mobile, and uses action-oriented copy gets clicked. If you're only going to test one thing, test your button.

Layout shapes how people read. Single-column layouts tend to outperform multi-column on mobile because they don't require zooming or horizontal scrolling. Readers scan emails in rough top-to-bottom patterns, so putting your most important content and CTA high up matters more than most senders realize. Inverted pyramid structure (big idea first, detail second, CTA last) works well for most email types.

Whitespace is doing more than you think. Crowded designs push people away. Generous spacing around text blocks and buttons helps readers focus on what matters. It's not about looking minimal. It's about reducing the visual load so the eye goes where you need it to go.

Images are a trade-off. Product shots and lifestyle photos can lift engagement, but image-heavy emails load slowly on poor connections and render as blank boxes when images are blocked (which happens more often than you'd expect). Human faces in images draw attention, but they also add file weight. A good rule of thumb is to make sure your email still makes complete sense with all images off.

Typography affects whether people actually read. Minimum 14px for body copy. 16px is safer for mobile. Dark text on a light background. Enough line spacing that sentences don't feel crammed together. These aren't style preferences. They're readability basics.

Color sets the mood and drives action. Your brand palette builds recognition. But button color is its own question. High contrast between the button and the surrounding background drives more clicks than the button color itself. A test where you change the button from gray to bright orange isn't testing color preference. It's testing contrast.

One thing worth knowing about all of this: A/B testing design elements works differently from testing subject lines. You need more volume to reach statistical significance because click rates are lower than open rates. And responsive design across devices means a layout that converts beautifully on desktop might fall apart on mobile, so always test across both.

Start with the variables closest to your conversion goal. Button design and placement first. Layout second. Typography and color third. Test one at a time, and let the results tell you what your audience actually responds to rather than what looks good in a preview window.

Not sure where your current design stands? Run it through our free accessibility checker to catch contrast and readability issues before you start testing.