About

Standard web design practices fail in the email environment. While modern browsers utilize Flexbox and Grid, email clients like Outlook for Windows rely on the Microsoft Word rendering engine, which only supports HTML3.2-era table structures. This tool solves the fragmentation problem by generating rigid, nested table hierarchies that force consistent layout behavior across 90+ email clients.

A critical failure point in modern branding is Dark Mode. When a recipient's device inverts color luminance, transparent PNG logos often disappear against the dark background. This generator implements a specific luminance_check logic, offering an automated "Safe Container" that preserves branding integrity without requiring separate assets. The output is a single, self-contained HTML block, sanitized of scripts and external stylesheets, ready for immediate deployment.

Formulas

To ensure the signature does not break the reading pane on mobile devices while maintaining structure on desktops, we calculate the maximum container width W_max. For Outlook, this must be defined in absolute points (pt) or pixels (px), not percentages.

W_max ≤ 600px

The contrast ratio CR for text legibility in Dark Mode is determined by the relative luminance L of the foreground and background colors. If the client inverts L_bg, the perceived contrast changes.

CR = L₁ + 0.05L₂ + 0.05

Our "Dark Mode Fix" applies a wrapper with a defined border-radius r and padding p to the logo image I to ensure L_bg remains high (white) locally around the brand mark.

style(I) =

{

border: 2px solid white if Mode == Darknone otherwise

Reference Data

Client / Feature	Render Engine	Flex/Grid	Background Images	Data URI (Base64)	Style Tag <style>	Media Queries
Outlook (Win)	Word	FALSE	FALSE (Requires VML)	FALSE	FALSE	FALSE
Apple Mail	WebKit	TRUE	TRUE	TRUE	TRUE	TRUE
Gmail (Web)	Gecko/Blink	FALSE	TRUE	FALSE (Blobs only)	TRUE	TRUE
Gmail (Android)	Android Native	FALSE	TRUE	FALSE	FALSE	TRUE
Outlook (Mac)	WebKit	TRUE	TRUE	TRUE	TRUE	TRUE
Samsung Email	Android Native	TRUE	TRUE	TRUE	TRUE	TRUE
Yahoo! Mail	Blink	FALSE	TRUE	FALSE	TRUE	TRUE
Thunderbird	Gecko	TRUE	TRUE	TRUE	TRUE	TRUE

Frequently Asked Questions

Outlook for Windows uses the Microsoft Word rendering engine, which does not support modern web standards like HTML5, Flexbox, or CSS Grid. It treats HTML like a Word document. iPhones use WebKit (like Safari), which supports modern CSS. This tool builds a "lowest common denominator" HTML structure using nested tables to force Outlook to behave like a modern browser.

Most enterprise email clients (Outlook, Lotus Notes) block external images by default to protect privacy. To mitigate this, we recommend using the "Alt Text" field for all images. This tool also offers a Base64 encoding option for icons, which embeds the image data directly into the code, bypassing the need for a server request in clients that support it (Apple Mail, Thunderbird), though Gmail and Outlook may still block it.

Email clients only universally support a small set of "Web Safe" fonts (Arial, Verdana, Times New Roman, Courier, Georgia). If you use a custom font (e.g., Google Fonts), it will only appear on Apple Mail and some web clients. For everyone else, it will fall back to the next font in your stack. We automatically generate a robust font-family stack (e.g., "Open Sans", Helvetica, Arial, sans-serif) to ensure the design degrades gracefully.

When a user switches to Dark Mode, the email client typically inverts colors: white backgrounds become black, and black text becomes white. However, a black logo (PNG) on a now-black background becomes invisible. Our "Dark Mode Fix" adds a conditional white background or a white stroke around your logo in the HTML code, ensuring it remains visible regardless of the recipient's theme settings.

Some email servers truncate emails that exceed a certain file size (e.g., Gmail clips messages over 102KB). While a signature is small, bloated code contributes to this limit. Our generator produces minified, inline-CSS HTML to keep the footprint as small as possible.