Introduction
Fonts in HTML email behave differently from fonts on the web. Email clients impose strict security and rendering constraints, limiting font support and leading to inconsistent results across platforms. This page explains how fonts work in HTML email and provides practical guidance for choosing and using fonts reliably.
Overview
Unlike web browsers, most email clients restrict how fonts are loaded and rendered. These restrictions are designed to protect users, improve performance, and maintain visual consistency within the email application. As a result, email clients may ignore specified fonts and replace them with fallback fonts without warning.
Font behavior can vary by client, operating system, and device. For this reason, font choices in email should prioritize readability and reliability over precise visual control.
Why font support is limited in email
Several factors contribute to limited font support in HTML email:
Security
Many email clients block externally loaded resources, including font files, to reduce security risks.
Performance
Mobile email apps prioritize fast loading and may avoid downloading additional assets such as custom fonts.
Consistency
Some clients enforce system fonts to align emails with the app’s native user interface.
Licensing
Not all fonts are licensed for embedding or redistribution in email content.
Because of these constraints, font substitution can occur at any time, even when a font is explicitly defined.
Recommended font usage
Use web-safe fonts
Web-safe fonts are preinstalled on most operating systems and are widely supported across email clients. They provide the most predictable rendering.
Common web-safe fonts include:
Arial
Helvetica
Verdana
Times New Roman
Georgia
Courier New
Define font stacks
Always define fallback fonts using a font stack. This allows the email client to select the first available font it supports.
Example:
font-family: Arial, Helvetica, sans-serif;If the preferred font is unavailable, the client moves to the next option in the list.
Use inline CSS
Font styles should be defined using inline CSS to maximize compatibility.
Define properties such as:
font-family
font-size
font-weight
font-style
Apply these styles directly to HTML elements rather than relying on embedded or external stylesheets.
Using custom fonts
Custom fonts can be used in HTML email, but support varies significantly.
Some email clients support custom fonts through
@font-faceMany clients ignore custom font declarations entirely and fall back to system fonts
Custom fonts should be treated as optional enhancements. Emails must remain readable and usable when a custom font is not applied.
Outlook limitations
Outlook on Windows does not support web fonts and ignores @font-face declarations. In these cases, Outlook applies a default system font.
This behavior cannot be controlled, which makes well-defined fallback fonts essential.
Font size and readability
Font choices should prioritize accessibility and legibility across devices.
Recommended practices include:
Use body text sizes that remain readable on mobile devices
Avoid very light font weights or decorative fonts
Ensure sufficient contrast between text and background
Visual styling should never compromise readability.
Testing and validation
Font rendering can differ widely between clients and devices. Always test emails across:
Common desktop and mobile email clients
Multiple operating systems
Light and dark display modes
Testing helps identify where fonts are replaced or rendered differently and ensures content remains readable in all environments.