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MailViewr - Free HTML Email Preview Tool
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AccuracyAbout

Test HTML & MJML Emails in Gmail, Outlook, Apple Mail Before You Send

Preview your email across Gmail, Outlook, and Apple Mail — desktop and mobile — before you send. Catch dark mode issues and get a full QA report.

How it works ↓
✓ 14 Email Clients✓ Dark & Light Mode✓ Pre-Send QA Report

Preview across real-world clients

See how the same HTML renders in Gmail, Outlook, Apple Mail, and more.

Catch layout breakages early

Spot spacing, alignment, and image issues before your audience does.

Move faster with fewer test sends

Iterate on your template without the 'send → check → fix' loop.

MailViewr SaaSBrowser - software database
#1 ChatGPT
FP#7 FounderPal
700+ active monthly users
49 countries

Trusted by developers at

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Free email preview tool showing HTML email test in Gmail and Outlook
Full Feature Suite

Everything you need to send email with confidence

Mailviewr Features

Email Client Coverage

  • Gmail, Outlook, Yahoo Mail — web, iOS, Android
  • Device simulation — desktop, tablet, mobile, orientation toggle

Rendering & Compatibility Testing

  • Dark mode preview and testing
  • CSS compatibility score with per-client error detection

Code Validation Tools

  • Inline CSS validation (style blocks + inline attributes)
  • CSS inlining

Pre-Send Quality Assurance

  • Send test emails to your inbox
  • Pre-Send QA Report — 9 checks, score out of 100

How it works

1

Paste your HTML or MJML

Paste your HTML or MJML email directly into the editor — MJML compiles to HTML in the browser. No signup required.

2

Choose an email client

Select Gmail, Outlook, Apple Mail, or a mobile device to test on.

3

Preview, fix & send

See exactly how it renders, check your compatibility score, toggle dark mode preview, and send a test email to your inbox—all before going live.

Free templates

DISCOVER
HANDY
TEMPLATES

Free HTML email templates with variables pre-tagged for Mailchimp, SendGrid, and Klaviyo. Preview in any email client before you send. Save time, look professional, and get perfect rendering every time.

See templatesCreate your own

NEWSLETTER

Newsletter Template

PROMOTIONAL

Promotional Email Template

WELCOME

Welcome Email Template

TRANSACTIONAL

Transactional Email Template

EVENT

Event Invitation Template

ANNOUNCEMENT

Product Announcement Template

→
View all
templates

ALL TYPES

Rendering Accuracy

See exactly
how it renders

35% of email opens now happen in dark mode. Every email client inverts colors differently — Gmail Android does full CIELAB inversion, Outlook applies partial overrides, Apple Mail uses HSL transforms. MailViewr runs each client's actual algorithm in your browser, so what you see matches what your subscribers see.

100%
Desktop accuracy (all clients)
90–95%
Light mode mobile accuracy
14
Client + theme combinations tested

Gmail Desktop

Chrome · Safari · Firefox

Dark mode97%
Light mode97%

Gmail Android

Mobile app

Dark mode~90%
Light mode97%

Gmail iOS

Mobile app

Dark mode75–80%
Light mode95%

Outlook Desktop

Chrome · Safari · Firefox

Dark mode100%
Light mode100%

Outlook Android

Mobile app

Dark mode~70% · beta
Light mode98%

Outlook iOS

Mobile app

Dark mode70–75% · beta
Light mode97%

Outlook mobile dark mode uses undocumented color override logic. Desktop and light mode accuracy is verified against real device recordings. How we measure accuracy →

Pre-Send QA Report
90/100
Issues Found2 checks failed · fix before sending
  • Gmail Clipping Risk
  • Unsubscribe Link Present
  • No Image-Only Content
  • Alt Text on All Images−5pts
  • No External Stylesheets
  • DOCTYPE Declaration
  • Structural Tags (html/head/body)
  • No Placeholder Hrefs−5pts
  • Viewport Meta Tag
SpamAssassin Score2.4 / 5.0  ✓ Pass

Pre-Send QA Report

Catch problems before you hit send

Run 9 structural checks and a SpamAssassin spam score analysis on your HTML email and get a readiness score out of 100. From Gmail clipping to missing unsubscribe links — see exactly what to fix, before your subscribers do.

Download your report as a professional PDF to share with teammates, clients, or stakeholders. Keep audit records before every send, and use reports for approval workflows and compliance reviews.

  • Gmail clipping risk (102KB limit)
  • Missing unsubscribe link (CAN-SPAM / GDPR)
  • Image-only email detection
  • Alt text on every image
  • No external stylesheet links
  • Placeholder href detection & link audit
  • Missing viewport meta tag
  • DOCTYPE declaration check
  • Structural tags (html / head / body)
  • SpamAssassin spam score + per-rule breakdown
  • Download PDF QA Reports
  • Share reports with clients & teams
  • Keep QA audit records
  • Professional email readiness reports
Run QA Report — it's free

Requires a free account · takes under 5 seconds

FAQ

Still have questions?

Everything you need to know about MailViewr. Can't find the answer? Email us directly.

General

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.

MJML

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 Rendering

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'.

Best Practices

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.

Technical

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.