Most of your campaign is read on a phone, often with images switched off, sometimes in dark mode. Designing for that is the difference between a campaign that works and one that looks fine on your desktop only.

Images

• Never put your message in a picture. Many mail clients block images by default; a text-in-image email arrives blank.
• Keep them a sensible size. A ten megabyte photo is slow on mobile data and can trip spam filters.
• Add alt text so there is something to read while images are blocked.
• Do not rely on a background image — support is patchy and it often just does not appear.

Dark mode

Many phones invert email colours. A logo saved as black text on a transparent background disappears entirely against a dark card. Use a version with a solid background, or one that works both ways.

The pre-send check

1. Send a test to yourself.
2. Open it on a phone. Is the main message visible without scrolling or pinching?
3. Turn images off, or look at it before they load. Does it still make sense?
4. Check every link goes where you think.
5. Read the subject line once more — it is the only part most people will ever see.