Your email looks different in Gmail, Outlook, Apple Mail, and on mobile — sometimes completely broken. Migomail previews your email across 90+ client and device combinations before you send, so design problems, rendering failures, and dark mode breakages are caught in testing, not in your subscribers' inboxes.
HTML email is not universal — the same code renders completely differently in Gmail, Outlook, Apple Mail, and on mobile devices. A design that looks perfect in one client may be completely broken in another. Migomail shows you every version before you send.
Preview your email across 90+ combinations of email clients, operating systems, and device types — Gmail (Web, iOS, Android), Outlook (2016, 2019, 2021, 365, Web), Apple Mail (Mac, iOS), Yahoo Mail, Samsung Mail, and more. Each preview is a real rendering from the actual client, not a simulation — generated by sending your email to a live instance of each client and capturing a screenshot.
Dark mode email rendering is one of the most inconsistent areas in all of HTML email — different clients invert colours, override backgrounds, and change text colour in completely different ways. Migomail generates a dark mode preview alongside each standard preview, so you can see exactly what your email looks like when a subscriber has dark mode enabled on Gmail, Outlook, or Apple Mail.
Over 60% of emails are opened on mobile devices. Migomail generates previews across all major mobile configurations — iPhone (small, large, plus), iPad, Android flagship, Android mid-range — in both portrait and landscape orientations, with both iOS Mail and Gmail app rendering shown for each device size.
Corporate email environments and some personal clients block images by default. An email where all images are blocked and there is no alt text becomes unreadable. Migomail generates an images-blocked preview showing exactly what your email looks like without images — forcing you to verify that alt text is present, CTAs are still visible, and the email communicates its message without images.
Alongside the visual previews, Migomail analyses your HTML for client-specific rendering problems — CSS properties not supported in Outlook, MSO conditional comments needed, VML fallbacks missing for rounded buttons, web fonts not loading in Gmail, and background images stripped by certain clients. The analysis maps each identified issue to the specific clients it affects.
The inbox view matters before the email is even opened. Migomail previews how your subject line and preheader appear in the inbox list view across different clients — checking for truncation at different display widths, showing how emoji render at various clients, and flagging subject lines that get cut off before the key message.
Compare two versions of your email side by side across all clients simultaneously — for example, compare the current version against a revised version with a different hero image or CTA layout. Changes that look identical in one client but render differently in another are immediately visible in the comparison view.
After making changes to your email template based on the preview results, regenerate all previews with a single click directly from the template editor — without leaving the campaign workflow. The preview panel updates with fresh screenshots within 2 minutes of triggering a regeneration.
The same HTML email renders differently across clients because each email client has its own rendering engine with its own CSS support, image-handling rules, and dark mode behaviour. Migomail shows you every version before you send.
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Not all CSS works in all email clients. Outlook's rendering engine (based on Microsoft Word's HTML engine, not a browser) is the most restrictive. Gmail strips certain properties. Knowing what is and is not supported prevents the most common class of inbox preview failures.
Dark mode email rendering is not a single standard — each client applies it differently. Gmail auto-inverts colours. Outlook partially inverts. Apple Mail applies a sophisticated transformation. The result: your carefully designed email can look completely broken in dark mode without the right CSS fixes.
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Migomail's dark mode preview shows you the "without fix" rendering so you can add @media (prefers-color-scheme: dark) rules to override Gmail and Outlook's auto-inversion for critical elements like your logo.
Inbox preview is built directly into the Migomail campaign builder — trigger previews at any point in your email build, not just at the pre-send review step.
A rendering failure in Outlook affects approximately 22% of subscribers. In Gmail on mobile, it affects 41%. In dark mode across all clients, it affects up to 82% of mobile openers. This is the revenue cost of untested rendering.
Feedback from email template designers, developers, and campaign managers who use Migomail inbox preview to catch rendering issues before they reach subscribers.
We are a B2B company and our subscriber base skews heavily towards corporate environments — which means a significant portion of our list uses Outlook, often 2016 or 2019, not the newer 365. Before Migomail inbox preview, we would design templates that looked perfect in Gmail and then discover post-send that the two-column layout was completely collapsed in Outlook 2016, putting all the content in a single narrow column in the top-left corner. It looked terrible. After our first preview test with Migomail showed us the Outlook failure, we spent one afternoon adding the right MSO conditional comments and table fallbacks. Our next campaign Outlook rendering rate went from "broken" to pixel-perfect. Our click rate in the Outlook segment increased by 34% in the following month.
The dark mode preview exposed something we had been sending broken for over a year. Our brand has a black logo on a white background. In light mode it looks great. In dark mode on Gmail, Gmail auto-inverts the white background to dark — so our black logo on white becomes black on dark background — essentially invisible. We had no idea this was happening because everyone on our team tests from Gmail on desktop in light mode. After Migomail's dark mode preview showed us the invisible logo, we added a CSS rule using prefers-color-scheme that wraps the logo in a white rounded rectangle in dark mode. Ten minute fix. But we would have kept sending that invisible logo to 70,000 subscribers indefinitely if the dark mode preview had not made it unmissable.
As an agency we now run Migomail inbox preview on every client campaign as a mandatory pre-send step — no exceptions. The time it saves on reactive fixes is the main value: one thorough preview test before sending is 20 minutes. One emergency investigation after a client calls to say their email looks broken in Outlook is half a day. More importantly, catching a broken rendering before it sends preserves client trust in a way that fixing it after the fact never fully does. The preview test is the single process change that has had the largest positive impact on our client satisfaction metrics in the past 12 months.
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Common questions about inbox preview and email client rendering.
Migomail's inbox preview uses real rendering — not simulation. Your email is actually sent to a live seed mailbox at each email client, and the email client renders it in a real environment (live browser for webmail clients, actual installed application for desktop clients, real device for mobile clients). A screenshot is captured from the rendered email and returned to your preview gallery. This is why the previews accurately show rendering differences that a CSS simulation would not catch — because Outlook's rendering engine, for example, has specific bugs and quirks that only appear when a real Outlook installation renders the HTML.
Outlook (desktop versions 2007–2021) renders HTML email using Microsoft Word's HTML rendering engine — not a browser engine like Chrome or WebKit. Word's HTML renderer was designed for word processing documents, not web content, and has very limited CSS support. It does not support border-radius (rounded corners), background-image CSS, flexbox, CSS grid, or position:absolute, among many other standard CSS properties. Outlook 365 (the web version) uses a browser-based renderer and has much better CSS support. Migomail's compatibility matrix shows exactly which properties are and are not supported in each version.
Dark mode rendering occurs when a subscriber has enabled a dark colour scheme on their device or email client. Different clients handle dark mode differently: Gmail on Android and iOS auto-inverts light colours and backgrounds to dark equivalents; Outlook partially overrides colours; Apple Mail applies a sophisticated transformation using CSS media queries. The result is that emails designed for light mode can look broken in dark mode — logos become invisible (dark logo on dark background), text becomes unreadable, and background colours invert unexpectedly. Since approximately 82% of mobile users have dark mode enabled, testing dark mode rendering is not optional for mobile-first email programmes.
Yes. The preview panel lets you select specific client groups — Desktop Only, Mobile Only, Dark Mode Only — or individual clients from a checkbox list. You can also create and save custom preview sets for your specific audience (for example, if your analytics show 80% Gmail + 15% Outlook, you can save a "My Audience" set with just those clients to run as your standard pre-send test). Running a partial preview set generates results faster and is suitable for most routine pre-send checks.
Under 2 minutes for most templates. Simple text-and-image emails typically complete in 60–90 seconds. More complex templates with multiple images or large inline CSS may take up to 2 minutes. Individual client previews appear as they complete — you do not need to wait for all 90+ to finish before reviewing the first results. Desktop client previews typically return first (30–45 seconds), followed by mobile, and dark mode screenshots arrive last.
Many corporate email environments block images by default as a security measure — images are not downloaded until the user explicitly clicks a button to load them. When images are blocked, an email that relies heavily on images for its content becomes unreadable. The images-blocked preview shows you exactly how your email looks when all images are suppressed — checking that your alt text is informative (not just the filename), that CTAs are visible and clickable even without the button image, and that your brand is still identifiable through text elements alone.
Yes. The preview comparison mode lets you select two saved versions of your email (for example, the current draft and a version where you changed the hero image or CTA layout) and display them side by side across all clients simultaneously. Differences that render identically across clients and differences that only appear in specific clients are immediately visible. The comparison view is useful for A/B test variant preview validation — you can confirm that both variants render correctly before launching the A/B test.
AMP for email is supported with Gmail AMP preview specifically — since AMP email is only supported by Gmail (and Yahoo in limited contexts), the preview shows both the AMP version (for subscribers whose Gmail client supports it) and the HTML fallback version (shown to all other clients and Gmail accounts where AMP is not enabled). This ensures you can verify both the interactive AMP experience and the fallback rendering that the majority of subscribers will still see.