How to check dark-mode and mobile previews?

Dark mode is now a real viewing context, not an edge case. About half your subscribers might see emails in dark mode, so you need to test for it. The problem is that dark mode varies wildly across email clients. What works on Gmail's dark mode might break on Apple Mail's. That's why you need specialized tools.

Litmus and Email on Acid both offer dark mode previews. You upload your email, and they show you how it renders when the system inverts colors. These automated previews catch the big issues: images turning invisible, text becoming unreadable, buttons disappearing. But here's the limitation. Automated tools show you the general picture. They don't catch every nuance. A brand color inverted might not look exactly right until you see it on an actual device.

That's where physical testing comes in. Keep at least one current iPhone and one Android device for final checks on critical campaigns. Rendering simulators are fast and cheap, but real devices show you how emails actually load on slow connections, how images appear on high-resolution screens, and how touch targets feel. For most sends, the automated preview is enough. For high-stakes campaigns, pair it with device testing.

Here's the workflow. First, build a testing matrix based on your audience data. If 40% of opens happen on iPhone in dark mode, that combination needs testing. Second, run your email through Litmus or Email on Acid and review the dark mode preview. Third, test on actual devices for the combinations that matter most. Check both iOS and Android native mail apps, plus Gmail's mobile app. They each render differently. That's pre-send testing done right.

Related: pre-send testing, dark mode testing, A/B testing.