Prioritise the clients your audience uses. A business audience may need careful Outlook testing; a mixed consumer list may need more coverage across Gmail, Apple Mail and mobile apps. If you have reliable information about your audience, use it to choose your tests.

Email HTML is not a normal website canvas. Start with the designer’s existing layout blocks and avoid copying complex web styling into a campaign. If you import custom HTML, use email-specific markup and test the delivered result.

The guide below is a design checklist, rather than a promise of identical support in every client version.

People should be able to understand the message and take the next step without zooming or struggling to tap a link. A simple structure is often easier to maintain across screen sizes than a dense newsletter.

• Keep headings short and body text comfortably readable.
• Give buttons and links space so they are easy to tap.
• Check that long URLs and headings do not force sideways scrolling.
• Use a reading order that makes sense when columns stack.
• Use descriptive links and meaningful alternative text.
• Check that the destination page works well on mobile too.

Check contrast and avoid using colour alone to explain a status or offer. Informative images need useful alternative text; purely decorative images can use empty alternative text. Keep the main action available as a readable link or button.

Email apps can treat dark mode differently. Some adjust colours automatically; others preserve more of the original design. Review the delivered message in both appearances where you can, especially logos, transparent images and text on coloured backgrounds.

A transparent dark logo may become hard to see against a dark background. Give important brand elements a suitable background and check that text remains readable if colours change. Do not assume a dark-mode preview in one app represents all inboxes.

The message should work without images

Some readers block remote images. Keep the offer, deadline and call to action in text, and test how image spaces and alternative text behave. Images should support the campaign rather than carry every essential detail.

Privacy settings also affect your reports

Apple’s Protect Mail Activity can download remote content in the background rather than when a person reads the email. As a result, a recorded open is not always evidence of a human read. Review clicks and campaign outcomes alongside opens.

Apple’s Mail privacy guidance ↗ · Explore Email Blaster analytics →

Animated GIF playback depends on the client, version and settings. Keep the first frame meaningful so a static view still communicates the main point. Avoid flashing content and use animation sparingly.

A linked video thumbnail is a dependable way to promote a video: show a useful still image with a play cue and link to the video page. Do not rely on an embedded player working inside every inbox.

Use a hosted page for forms or interactive experiences that need broad availability. Ordinary marketing emails should not depend on JavaScript or an iframe to deliver their essential content. Specialised interactive formats have their own requirements and limited support, so treat them as enhancements with a normal HTML fallback.

When a deadline matters, include the actual date and time in readable text. A countdown image can become stale or fail to update, so it should not be the only way the reader understands the offer.

Email Blaster’s designer provides desktop, mobile and tablet preview options. Use these to review the campaign’s layout and reading order as you work.

A device preview is useful, but it is not proof of identical rendering in every email app. Send a test campaign to the inboxes that matter to your audience, including separate tests for classic and new Outlook where relevant.

1. Check the design: review text size, spacing, images and the main action.
2. Send the test: open the delivered message in representative desktop and mobile clients.
3. Change settings: review dark mode, blocked images and narrow reading panes where available.
4. Follow the links: check buttons, destination pages, reply details and the unsubscribe route.
5. Repeat after edits: changes to content or layout can introduce new problems.

Forwarding an email can change its HTML. Test a direct campaign delivery rather than relying only on a forwarded copy. For a complex custom design, consider a specialist rendering test service alongside your own inbox checks.