MJML: the established markup framework for bulletproof email HTML

Nobody writes email HTML by hand for long before they start hating it. Tables inside tables, every style attribute inlined by hand, a different fix for every client, and one Outlook quirk that undoes the fix you just made. MJML was built to remove that entire layer of pain: you write semantic markup, and the compiler produces the bulletproof table soup underneath.

Why it made the cut

MJML is the most established open-source email markup framework going, and it is worth knowing even if you end up choosing something else, because a huge share of the template ecosystem, tutorials, agency boilerplates, and third-party builders assumes it. Instead of <table> and inline style="", you write <mjml>, <mj-body>, <mj-section>, <mj-column>, <mj-text> and so on: semantic tags that transpile to the same responsive, tested HTML that survives Gmail, Outlook and everything in between. It has editor integrations for VS Code and Sublime Text, so you get live preview and linting as you write, and a template ecosystem that has had a decade to accumulate.

How to use it

Install the CLI or the editor extension, write your email in MJML tags, and compile to HTML either from the command line, a build script, or directly in the editor preview. The compiled output is plain HTML you can paste into any sending provider.

Worth knowing

MJML is free and MIT licensed, currently at v5.4.0 (released 29 June 2026, the 126th release), with 18.2k stars on GitHub. It was created by Mailjet in 2015 and is still maintained under the mjmlio organisation, so this is not an abandoned side project, it has a long, continuous maintenance history behind it. Source and docs at the link below.