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MJML (Mailjet Markup Language) is an open-source markup language designed to simplify the creation of responsive HTML emails. It abstracts away the complex table-based layouts and inline CSS required for cross-client email compatibility, allowing developers to write clean, semantic code that compiles into fully responsive email HTML.
Building responsive marketing email templates that work across all major email clients
Creating transactional email templates for order confirmations and shipping notifications
Developing email design systems with reusable components for consistent branding
Rapid prototyping of email designs for stakeholder review and approval
Migrating legacy email templates to a modern, maintainable codebase
Generating email templates programmatically for personalized content at scale
Training non-developers to create professional email templates without HTML expertise
Building white-label email template libraries for SaaS platforms and agencies
Email HTML development is notoriously difficult because email clients render code inconsistently. Unlike web browsers that follow modern standards, email clients like Outlook still use legacy rendering engines that require table-based layouts and inline CSS. Writing and maintaining this code manually is time-consuming and error-prone, often taking hours to create a single responsive template. MJML dramatically reduces email development time by abstracting away these complexities. What might take a developer 4-6 hours to code manually can be accomplished in 30-60 minutes with MJML. This efficiency gain allows marketing teams to iterate faster on email designs and launch campaigns more quickly without sacrificing quality or cross-client compatibility. For email marketing operations, MJML ensures that every email renders correctly regardless of whether recipients open it in Gmail on mobile, Outlook on desktop, or Apple Mail on iPad. This consistency improves brand perception and engagement metrics, as broken layouts can cause recipients to ignore or unsubscribe from emails.
MJML operates as a transpiler that converts its simplified markup syntax into production-ready HTML email code. Developers write email templates using MJML's component-based tags such as mj-section, mj-column, and mj-text, which mirror common email layout patterns. The MJML engine then processes this code and generates the complex nested table structures, media queries, and inline styles required for consistent rendering across email clients. The framework includes a comprehensive library of pre-built components covering headers, footers, images, buttons, social icons, and more. Each component is designed with email best practices baked in, automatically handling quirks of different email clients like Outlook, Gmail, and Apple Mail. MJML can be used via command-line tools, Node.js packages, or online editors, integrating seamlessly into development workflows. MJML also supports custom components and theming, allowing teams to create reusable design systems for their email templates. Variables and includes enable template composition, making it easy to maintain consistency across multiple email campaigns while reducing code duplication.
Use MJML's built-in components instead of custom HTML to ensure cross-client compatibility
Test compiled output in multiple email clients using tools like Litmus or Email on Acid
Keep templates modular by using mj-include for reusable header and footer sections
Define brand colors and fonts as MJML attributes to maintain design consistency
Optimize images before embedding and always include alt text for accessibility
Use mj-preview to control the preview text shown in email client inboxes
Set fallback fonts for web fonts since many email clients don't support custom fonts
Version control your MJML source files separately from compiled HTML output
Yes, MJML is completely free and open-source under the MIT license. You can use it for personal and commercial projects without any cost. Mailjet maintains the project but does not require you to use their email sending service.
MJML is designed to produce HTML that renders correctly in all major email clients including Gmail, Outlook (desktop and web), Apple Mail, Yahoo Mail, and mobile email apps. The framework is continuously updated to address new client quirks and rendering issues.
Yes, MJML compiles to standard HTML that works with any email sending service. You can use the compiled output with Mailchimp, SendGrid, HubSpot, Amazon SES, or any other ESP that accepts HTML email templates.
MJML offers more flexibility and control than drag-and-drop builders while remaining easier than raw HTML coding. It's ideal for developers and technical marketers who want custom designs without the limitations of visual builders, though it does require basic coding knowledge.
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