Email Compatibility Solutions

Bulletproof Outlook fixes for the email clients that refuse to play nice.

Outlook for Windows still uses Microsoft Word as its rendering engine. Our solutions generate VML fallback code so your buttons, backgrounds, and layouts render identically — in Outlook, Gmail, Apple Mail, and everywhere else.

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Bulletproof Button Generator

Generate VML email buttons that render in every Outlook version — including the Word-based renderer that breaks border-radius and padding.

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Outlook Background Generator

Build bulletproof Outlook background images with VML fallback so hero banners look identical in Outlook, Gmail, and Apple Mail.

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Outlook HTML Sanitizer

Fix the most common Outlook rendering issues: collapsing margins, ghost spacing, divider lines, and font fallbacks — in one click.

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EML File Viewer

Open any .eml file from Gmail, Outlook, Apple Mail, or Thunderbird in your browser, then download the email as a PDF, PNG, or JPG.

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Pixel Converter

Convert pixels to CSS units (em, rem, pt, vh) and physical measurements (inch, cm, mm), plus A/B/C/US paper sizes to pixels — with live reference tables.

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What "bulletproof" actually means in email

"Bulletproof" is the industry term for an email element that renders identically across every major client without relying on optional CSS. A bulletproof button degrades gracefully — modern clients use CSS, Outlook for Windows falls back to VML, plain-text clients see clean anchor text. No broken padding. No missing hero image. No CTA that disappears in Outlook.

EMLinter's solutions generate the bulletproof code for you. Pick the element you need — button, background, sanitizer — fill in the inputs, and copy the output. No VML syntax to memorize, no Outlook conditional comments to hand-roll.

Outlook & Email Compatibility FAQs

Microsoft Outlook for Windows (2007–2024) uses the Microsoft Word rendering engine instead of a real browser engine. That means CSS3 properties like border-radius, background-image, padding on <a> tags, and modern fonts are silently ignored. Bulletproof code uses VML — Microsoft's legacy XML format — as a conditional fallback so the design still renders pixel-perfect.
VML (Vector Markup Language) is a Microsoft-specific XML language for vector graphics. It is wrapped in <!--[if gte mso 9]> conditional comments so only Outlook reads it; every other client ignores the block entirely. Yes — it is still the only reliable way to get rounded-corner buttons and full-bleed hero backgrounds in Outlook for Windows, and that engine is not going away soon.
Slightly — usually under 200 bytes per VML block. That is well worth it given Outlook still represents 8–15% of B2B email opens. Use the EMLinter HTML Email Minifier to strip whitespace afterward and you will reclaim most of the added size.
Outlook for Mac and Outlook.com use a WebKit-based engine and render modern CSS fine, so the VML fallback is invisible there. Our generators produce code that degrades cleanly: modern clients use the CSS path, Outlook for Windows uses the VML path. You ship one HTML file that works everywhere.
Partly. Outlook.com and Outlook for Mac use a WebKit engine, so our Dark Mode Tester and the live previews in the Outlook generators will closely match what those clients show. For Outlook for Windows specifically, you need a Windows machine, a VM, or a paid service like Litmus or Email on Acid — there is no free way to simulate the Word renderer.
Yes. Edit your template in our Visual Editor or fix it with our Outlook solutions, then copy the HTML and paste it directly into Mailchimp, Klaviyo, HubSpot, Campaign Monitor, Salesforce Marketing Cloud, ActiveCampaign, Brevo, or any other ESP that accepts custom HTML.