Definition
A desktop email client is software installed directly on a computer that manages and reads email, such as Microsoft Outlook, Apple Mail or Mozilla Thunderbird. It connects to your mail server and stores or caches messages locally.
Desktop clients differ from webmail in how they render email, and each has its own quirks. Because desktop clients often rely on legacy HTML rendering engines — Outlook especially — emails can display differently there than in webmail. Designers must account for these differences to ensure consistent appearance.
Common Desktop Clients
| Client | Notes |
|---|---|
| Microsoft Outlook | Uses a limited rendering engine |
| Apple Mail | Renders modern HTML well |
| Mozilla Thunderbird | Flexible and standards-based |
| Others | Vary by platform |
Each renders email its own way.
Desktop vs Webmail
| Factor | Desktop Client | Webmail |
|---|---|---|
| Location | Installed on the computer | In the browser |
| Rendering | Varies, often dated engines | Modern web standards |
| Storage | Local cache | Server-based |
Rendering differences matter to designers.
Designing for Desktop Clients
- Test in the client: Verify appearance in the relevant software.
- Use fallbacks: Safe styling for limited renderers.
- Check images and fonts: Confirm they behave as intended.
- Account for Outlook: Optimise for its restricted engine.
Related Glossary Terms
Above the Fold in Email
Above the fold in email refers to the content visible to a recipient before they scroll, a critical area for first impressions and primary calls to action.
Accessible CTA (Email)
An accessible CTA is a button or link coded with sufficient colour contrast, visible focus states, descriptive screen-reader text, and a minimum touch target of 44×44 pixels.
Adaptive Design
Adaptive design in email uses predefined layouts that adjust to specific device or client widths, rather than fluidly resizing to every possible screen.
AI-Generated Content in Email
AI-generated content in email is copy, images, code or subject lines produced by artificial intelligence tools to speed up campaign production and testing.
AI Inbox
An AI inbox is an email client that uses artificial intelligence to summarise, sort, prioritise and sometimes answer emails before the human recipient reads them. It is transforming email marketing metrics and copywriting.
Alt Text
Alt text is the written alternative to an image in an email, displayed when images are blocked, slow to load, or consumed by screen readers.
Frequently Asked Questions
A desktop email client is software installed on a computer that manages and reads email, such as Outlook, Apple Mail or Thunderbird. It connects to your mail server and keeps messages locally.
Webmail runs in a browser using modern web rendering, while a desktop client is installed software whose rendering engine can be older and more limited — Outlook especially. This means the same email can look different between the two.
Outlook uses a legacy HTML rendering engine that supports a limited set of modern CSS. Layouts that work in webmail or Apple Mail may break or shift in Outlook, so designers add fallbacks and test specifically in that client.
Test your email in the desktop clients your audience uses, apply fallback styling for limited renderers, and give special attention to Outlook's restricted engine. Prefer simpler, well-supported HTML that displays consistently.