---
title: "HTML Email Resources: 20 Tools, Frameworks and Specs"
description: An HTML email is a message with an HTML body styled by inline CSS. These 20 resources cover client support, frameworks, inliners and testing.
canonical: https://sendhq.cc/blog/html-email
last-updated: 2026-11-05
author: Dhrumil Barot
author_bio: Dhrumil is an email marketing expert. Dhrumil built SendHQ so developers and AI agents can send, receive and track email without fighting deliverability on their own.
published: 2026-11-05
updated: 2026-11-05
---
# HTML Email Resources: 20 Tools, Frameworks and Specs
By [Dhrumil Barot](https://sendhq.cc/about.md#founder), Founder
An HTML email is a message with an HTML body styled by inline CSS. These 20 resources cover client support, frameworks, inliners and testing.
Published November 5, 2026 · Updated November 5, 2026
**TL;DR:** An HTML email is a message whose body is written in HTML and CSS instead of plain text, usually sent next to a plain-text copy. Building one well needs four kinds of resource: a client support table (Can I email), a framework (MJML, Maizzle or React Email), a CSS inliner (Juice) and a test tool (Mailpit locally, Parcel or Mailgun Inspect for client previews).
An HTML email is an email whose content is an HTML document, so it can carry layout, colours, images, buttons and links, while a plain-text email carries only characters. The HTML email format is a MIME message: the HTML body and a plain-text fallback sit side by side in a `multipart/alternative` part, defined in [RFC 2046](https://www.rfc-editor.org/rfc/rfc2046) in 1996, and the reader's client shows the richest version it supports. The hard part is that every client renders HTML differently: Gmail ignores CSS it does not support, classic Outlook for Windows uses its own engine with partial `")` returns ``. It flattens modern CSS nesting before inlining. Run it in your build, not by hand.
- [Lee Munroe's responsive template](https://github.com/leemunroe/responsive-html-email-template): free, MIT. One clean template with a call-to-action button, shipped in both `email.html` and `email-inlined.html`, so you can see exactly what inlining changes. Its README states the rule plainly: if you send through an API, inline before sending.
```
import juice from "juice";
const html = juice(rawTemplateHtml, { preserveMediaQueries: true });
// send `html` as the html body, plus a text version
```
The style attribute survives clients that strip the head.
## How do I test rendering across mail clients?
Test in two layers: capture every message locally while developing, then preview in real clients before a template ships.
- [Mailpit](https://mailpit.axllent.org/): free, open source, single binary or Docker image. A fake SMTP server with a web UI, an HTML compatibility checker against common clients, a link checker, SpamAssassin or Rspamd scoring and a REST API for integration tests. The best free default for local development.
- [Parcel](https://parcel.io/pricing): a code editor built for email. The Community plan is $0 (50 emails, HTML problem checking, previews); Pro is $29 per user per month. It also publishes free tools such as an EML viewer.
- [Mailgun Inspect (formerly Email on Acid)](https://www.emailonacid.com/pricing/): screenshots in 100+ clients and devices. Basic is $99 a month for 1,000 previews, Premium $199 for 2,000, $0.15 per extra preview (prices checked November 2026). Worth it when a broken Outlook render costs you real money.
- [Litmus](https://www.litmus.com/pricing): the other long-standing preview suite, now part of Validity Engage; pricing is quote-based. Its blog and dark mode guides are useful even without an account.
Before relying on previews, check the message size: Gmail clips messages over roughly 102KB and hides the rest behind a "View entire message" link ([Email on Acid](https://www.emailonacid.com/blog/article/email-development/gmail-clipping/)), which can hide your footer and unsubscribe link. Bloated inlined CSS and whitespace from templating engines are the usual causes.
## Code references and learning
- [Good Email Code](https://www.goodemailcode.com/): free, by Mark Robbins. Copy-paste base template, preview text, button-styled links and spacing, each with the reasoning behind it, plus accessibility notes on headings, ARIA landmarks and `rem` units.
- [Parcel's Learn Email course](https://parcel.io/): free course on the foundations of HTML and CSS for email, from the same team as the editor.
- [RFC 2046](https://www.rfc-editor.org/rfc/rfc2046): the MIME media types spec. Read the `multipart/alternative` section once and multipart bugs stop being mysterious.
- [SendHQ email templates](https://sendhq.cc/templates.md): free, ready transactional layouts (receipt, password reset, magic link, verification, welcome) to start from, with a [responsive design guide](https://sendhq.cc/guides/email-responsive-design-template).
## Where should a beginner start?
1. Read Good Email Code's base template and copy it as your skeleton.
2. Check every CSS property you plan to use on Can I email.
3. Build your first template in MJML (markup) or React Email (TypeScript), whichever matches your stack.
4. Inline with Juice, or let the framework's build do it, and generate a plain-text version.
5. Send it to Mailpit locally and fix what its compatibility checker flags.
6. Before launch, preview in Gmail, Apple Mail and classic Outlook with Parcel or Mailgun Inspect, and keep the message under 102KB.
## From template to production sending
Once templates render, the next problem is operating them: which version a customer actually received, and what happens when a variable is missing. [SendHQ](https://sendhq.cc/index.md) hosted templates declare typed variables, reject a render with a 422 when data does not match, escape inserted values by context, and record the published release and a rendered-content hash on every send, so a support ticket about a broken receipt traces back to the exact HTML that went out. If your mail is mostly transactional, our [transactional vs marketing email guide](https://sendhq.cc/guides/transactional-email-vs-marketing.md) explains why it belongs on a separate stream.
## FAQ
### What is an HTML email template?
An HTML email template is a reusable HTML email layout with placeholders, such as `{{first_name}}` or an order total, that your code or email service fills in at send time. Good templates are table-based, have CSS inlined, include a plain-text version and are tested in the major clients.
### Is HTML email better than plain text?
Neither is better for every message. HTML supports branding, buttons and tables such as receipts; plain text is lighter and looks personal. Send both in one `multipart/alternative` message so each client shows what it supports.
### Can I use JavaScript or forms in HTML email?
No. Mail clients strip JavaScript and generally block forms for security, so interactive behaviour must be a link to a web page.
### Why does my HTML email look broken in Outlook?
Classic Outlook for Windows (2007 to 2019 versions) renders HTML with a limited engine: partial `