Previewing in dark mode
Dark mode is the most common reason a campaign looks wrong in a real inbox. Here is what mail apps change, what to look for in Inbox Lab, and how to fix the usual problems.
A large share of your recipients read email on a phone with dark mode switched on. Their mail app does not simply show your campaign on a dark background; it rewrites colours. Light backgrounds become dark, dark text becomes light, and anything that relied on the original combination can become unreadable or disappear. Inbox Lab simulates this so you see it before your recipients do.
What mail apps actually do
There is no single dark mode. Some apps leave your colours alone. Some invert only the background and keep your text. Some fully invert everything, including images with transparent backgrounds. Inbox Lab applies the common approach: dark page and content backgrounds, light text, and muted image placeholders. It will not match every app pixel for pixel, but it reveals the failures that occur in most of them.
Opening the preview
In the Preview step, choose Mobile and switch the mode to Dark. Then switch Images Off. Those two combinations, dark mode on a phone and images blocked, are where most layout complaints come from. Scroll the whole campaign; problems often appear in the footer or in a section you did not change.
The five things to look for
- Logos that vanish. A dark logo on a transparent background disappears against a dark surface. Use a logo with a light version, or place the logo on a solid, branded background block.
- Text set in near-black on a coloured background. If the app inverts the text but not the background, you get light text on a light colour. Prefer text on neutral backgrounds, or use strong contrast in both directions.
- Buttons that lose their edges. A button whose background matches the inverted surface becomes invisible. Give buttons a brand colour that reads on both light and dark surfaces, and keep a visible border or padding.
- Images with white backgrounds. A product photo on a white square becomes a bright block on a dark page. Where you can, use images with transparent or neutral backgrounds, or accept the look and make sure the alt text explains the image.
- Divider lines that disappear. Light grey dividers vanish on dark backgrounds. Use dividers with mid-tone colours or rely on spacing instead.
Fixing issues in Studio
Most fixes are block settings rather than redesigns. Select the block in Studio and adjust its background, text colour or padding. For the logo, use the brand kit to add a light variant and choose it in the logo block. For buttons, keep the brand primary colour and let Studio render the Outlook-safe markup. Campaign Guardian also checks text contrast in both light and dark mode and lists any block that falls below a readable ratio, with a direct link to that block.
Images off
With images off, your campaign is only text and structure. Every image block shows its alt text, and every image without alt text shows an empty box. Write alt text that carries the message, not a filename: Spring collection, 20% off until Sunday rather than hero-final-v3. Avoid using an image for the main call to action; a real button block works with images off and in dark mode.
Make it a habit
Check dark mode and images off on every campaign, not just the first one. Content changes move blocks around, and a footer that was fine last month can break when a new section is added above it. The check takes a minute in Inbox Lab, and Guardian will remind you if contrast slips.