Webmail Providers Supporting Inline AVIF Images

AVIF (AV1 Image File Format) offers superior compression and visual fidelity compared to traditional formats like JPEG and WebP, making it an attractive choice for email marketers looking to boost load speeds. However, support across major webmail clients is fragmented due to varying backend image proxies and rendering engines. While web browsers universally handle AVIF, webmail clients often preprocess, cache, or block unsupported image types, directly impacting whether inline AVIF graphics display in an inbox.

Outlook.com (Microsoft 365 Web)

Outlook on the web renders inline AVIF images properly, provided the subscriber accesses their inbox through an AVIF-compatible browser such as Google Chrome, Microsoft Edge, Mozilla Firefox, or Safari. Because Microsoft's webmail interface relies directly on standard web platform rendering rather than a restrictive transcoding proxy, inline AVIF marketing images generally display without issue.

Yahoo Mail and AOL

Both Yahoo Mail and AOL support inline AVIF imagery on desktop and mobile webmail. Their image-caching infrastructure permits the AVIF format to pass through to the client without forcing conversion to older image formats or blocking the payload, assuming the user's browser supports modern codecs.

Gmail (Google Workspace)

Gmail currently does not reliably support inline AVIF images. Gmail routes all external imagery through the Google Image Proxy to protect user privacy and cache assets. This proxy frequently fails to process or correctly serve AVIF files, resulting in broken image icons or failed downloads. Marketers should avoid sending standalone AVIF images to @gmail.com and Google Workspace addresses.

Apple iCloud Mail

iCloud Mail accessed via the web supports inline AVIF images, provided the user is browsing on a platform with native AVIF decoding (such as Safari 16+ on macOS/iOS, or modern releases of Chromium-based browsers). iCloud does not utilize an aggressive image proxy that strips modern media types.

Privacy-Centric Webmail (Proton Mail, Fastmail)

Proton Mail and Fastmail both support inline AVIF images in their web interfaces. Neither platform utilizes transcoding proxies that alter file formats, meaning the client defers image decoding directly to the subscriber's browser.

Best Practices for Email Deployment

Because Gmail commands a massive share of the webmail market and lacks reliable AVIF support, inline AVIF files should never be deployed as standalone <img src="..."> assets. Email developers should use the HTML <picture> element to serve AVIF with fallbacks: