AVIF Support in Email: Newsletters and Attachments

This article examines how modern email clients handle AVIF (AV1 Image File Format) files, covering both inline graphics within HTML newsletters and standalone file attachments. While AVIF provides superior compression and visual fidelity compared to JPEG and WebP, its adoption across email ecosystems remains fragmented. Below is a breakdown of current rendering capabilities across major providers, operating system preview behaviors for attachments, and essential fallback strategies for email marketers.

AVIF in HTML Newsletters

Rendering embedded images within HTML campaigns requires compatibility from both the email client’s rendering engine and any intermediary image-caching servers.

• Apple Mail (iOS, iPadOS, macOS): Apple Mail offers the most robust support. Devices running iOS 16, iPadOS 16, and macOS Ventura (or later) use modern WebKit engines that natively render AVIF images embedded via standard <img> or <picture> tags.
• Gmail: Gmail routes external images through Google’s Image Proxy. The proxy frequently fails to decode or cache AVIF files properly, often resulting in broken image icons or outright dropping the image. Furthermore, Gmail automatically strips the HTML5 <picture> tag, making progressive enhancement difficult within this client.
• Microsoft Outlook: Support depends heavily on the specific client version. Legacy Outlook for Windows (2016, 2019, 2021) uses the Microsoft Word rendering engine, which has no support for AVIF. The "New Outlook" for Windows and Outlook on the web leverage Chromium-based rendering, which technically supports AVIF if the underlying browser does, though proxy and security policies can still block the assets.
• Yahoo Mail and AOL: Webmail versions support AVIF when accessed through modern browsers (Chrome, Firefox, Safari, Edge). However, mobile application support varies based on the device's default Webview components.

AVIF as Email Attachments

When an AVIF file is sent as a MIME attachment (image/avif) rather than linked inside an HTML template, the handling shifts from email rendering engines to operating system capabilities:

• File Delivery: All major email servers transmit AVIF attachments without corruption, treating them as valid binary payloads.
• Thumbnail Previews: In-client previews depend on the operating system. Apple devices (iOS 16+ and macOS 13+) and modern Android versions display visual thumbnail previews directly in the client. Windows systems generally display a generic file icon unless the user has installed the AV1 Video Extension from the Microsoft Store.
• Saving and Opening: Regardless of preview support, recipients on any platform can download the file to open it in a compatible viewer or web browser.

Best Practices for Implementation

Because global email support for AVIF remains limited, sending AVIF as a primary image format without contingencies is not recommended for production campaigns.

To safely utilize AVIF, employ progressive enhancement with standard fallbacks:

<picture>
  <source srcset="image.avif" type="image/avif">
  <source srcset="image.webp" type="image/webp">
  <img src="image.jpg" alt="Description" width="600" style="display: block; width: 100%; max-width: 600px;">
</picture>

For environments like Gmail that ignore <picture> tags, the parser defaults directly to the <img> tag, ensuring the legacy JPEG or PNG displays properly. Until webmail proxies and corporate desktop clients universally adopt the AV1 codec, AVIF should only be deployed as an optional enhancement layer alongside traditional formats.