It helps you see how your HTML email will look in different email clients and devices before you send it. This eliminates guesswork and reduces the risk of sending broken emails.

Yes! MailViewr is completely free. You can preview your HTML emails across multiple clients without any cost or signup required.

No account is required. Simply paste your HTML and start previewing immediately.

Yes. Paste your MJML and MailViewr compiles it to HTML in your browser, then previews how it renders across Gmail, Outlook, Apple Mail and mobile — including dark mode.

It does. MailViewr compiles MJML to email-ready HTML in the browser using the official MJML engine. You can preview the result, run a QA report, and download the generated HTML.

Yes. After compiling, MailViewr previews the HTML in Outlook (desktop and mobile) alongside Gmail and Apple Mail so you can catch Word-engine rendering issues before you send.

It's completely free with no signup. Your MJML is compiled entirely in your browser and is never uploaded to a server just to preview it.

Email clients don't share the same HTML/CSS support. Outlook desktop uses Microsoft Word's rendering engine, which ignores many modern CSS properties like flexbox, grid, and certain padding/margin rules.

MailViewr supports previews for Gmail (web, Android, iOS), Outlook (desktop, web, mobile), Apple Mail, Yahoo Mail, and other popular clients.

Some email clients automatically invert or adjust colors in dark mode to improve readability. This can affect backgrounds, text, and images. Always test dark mode previews to ensure your design remains readable.

Most email clients don't support web fonts. Gmail, Outlook, and Yahoo will fall back to system fonts. Always specify fallback font stacks like 'Arial, Helvetica, sans-serif'.

Those previews often represent devices, not real client rendering quirks. Client-specific previews reveal where Gmail vs Outlook behaves differently, catching issues ESP previews miss.

Start with a high-impact combo: Gmail (mobile) and Outlook (desktop). If it works there, you'll catch most common breakages early. Then expand to Apple Mail and other clients.

Tables are still the most reliable choice for email layouts. While modern clients support divs, Outlook desktop requires table-based layouts for consistent rendering.

Use fluid tables with percentage widths, media queries where supported, and mobile-first design. Test thoroughly since media query support varies by client.

Yes, MailViewr will load and display external images in your preview. Make sure your image URLs are accessible and use HTTPS for best compatibility.

No. Your HTML is processed locally in your browser and is not stored on our servers. Your email content remains private.

Avoid flexbox, grid, position: absolute/fixed, advanced selectors, and CSS variables. Stick to inline styles, basic padding/margin, and table-based layouts for maximum compatibility.

Yes. The Pre-Send QA Report includes a SpamAssassin spam score check. SpamAssassin is the industry-standard open-source spam scoring engine used by most mail servers. MailViewr runs your HTML through it and returns your score, the 5.0 pass/fail threshold, and a per-rule breakdown so you can see exactly what's triggering flags.

Aim for under 2.0 — that's considered clean. Scores below 5.0 pass most mail servers' default threshold. Scores between 5.0 and 7.9 will be flagged or filtered, and scores of 8.0 or above are typically rejected outright. The SpamAssassin check is included free in every QA Report.

These are expected when testing in a preview tool. MailViewr submits your HTML directly — not through an SMTP server — so there are no routing headers, timestamps, or Message-ID headers. Real sends via any ESP (Mailchimp, SendGrid, etc.) automatically add these headers, so they won't fire on actual campaigns. They carry 0 or negative scores and are flagged as expected in the results panel.

No. The SpamAssassin check is a separate, informational section. Only the 9 structural checks (Gmail clipping, missing unsubscribe link, alt text, etc.) contribute to your score out of 100. The spam score is shown alongside so you have the full picture before sending.

BAYES rules are SpamAssassin's Bayesian classifier — it analyses word patterns in your email statistically. BAYES_00 means it's 99%+ confident the email is not spam (very beneficial). BAYES_99 means it's almost certain it is spam. For marketing emails, keeping your content clear and avoiding spam-like language helps keep the Bayesian score low.

URIBL_BLOCKED means a DNS blocklist query was blocked by the server environment — it does not mean your domain is on a blocklist. This is a common result in sandboxed or preview environments like MailViewr and is not a real spam signal for your email. It should be ignored for testing purposes.