If you’ve migrated from Classic Outlook and noticed that some image formats now behave differently — iPhone photos that won’t preview, AVIF files that arrive as attachments instead of inline, the occasional WebP that just works without doing anything special — none of that is random. It’s a direct consequence of how New Outlook is built.

Classic Outlook is a Win32 application. When it needs to display or send an image, it goes through MAPI and the same Windows imaging codec stack that the Photos app uses. New Outlook is a web application running inside a WebView2 host. When it needs to display or send an image, it goes through the same codec path that Edge uses to render a webpage. That sounds like a small architectural detail. It is the cause of every format-specific behaviour difference between the two clients, and once you understand it, the rest of this article is a series of predictable consequences rather than a list of mysterious bugs.

This is the format-by-format situation in New Outlook for Windows as of May 2026.

HEIC and HEIF (iPhone photos)

This is the format people ask about the most, because every iPhone in the world saves photos as HEIC by default unless the user has gone into settings and changed it.

In New Outlook, HEIC inline display can work, but it depends entirely on what’s installed on the machine. The codec is not bundled with Windows. To make HEIC images render anywhere on Windows — including New Outlook — you need the HEIF Image Extensions from the Microsoft Store. That extension is free. With it installed, HEIC images dragged or pasted into a New Outlook compose window render inline correctly. Received HEIC attachments preview correctly. Without it, you get a broken image placeholder and your recipient sees nothing useful either.

The catch is that HEIF Image Extensions depends on the HEVC video codec to actually decode the file. Microsoft splits these into two Store packages. HEIF Image Extensions is free. HEVC Video Extensions is £0.99. Most modern Windows 11 machines that came pre-installed with an OEM build have HEVC already included. Custom builds and many corporate images do not. If HEIF Image Extensions is installed but HEIC still won’t render, the missing piece is HEVC.

There’s a free OEM version of HEVC Video Extensions that Microsoft makes available through a different Store link, and which is functionally identical. We cover the paid-versus-free decision in detail in the HEVC Video Extension question. For New Outlook specifically, install both, and HEIC will work consistently inline.

When you send HEIC to a recipient who doesn’t have these extensions installed — likely most non-Apple-ecosystem users outside corporate Windows fleets — the attachment will land as a file but the inline preview will fail at their end. This is not New Outlook’s fault. It is the consequence of HEIC being an Apple-ecosystem format with patchy support outside it. If you’re sending photos to a mixed audience, convert to JPEG before sending. Windows 11’s built-in Photos app can do this; right-click any HEIC and Open with → Photos, then Save a copy as JPEG.

WebP

WebP is the format that just works in New Outlook, and the reason it just works is exactly the architecture point made above. The WebView2 engine has had native WebP support for years — it’s the same Chromium engine that decodes WebP for every webpage you load in Edge. So when a WebP image is pasted, dragged, or received in New Outlook, the editor doesn’t need to ask Windows to install a codec. It already has one.

This is one of the rare cases where New Outlook is more capable than Classic Outlook out of the box. Classic Outlook needed the WebP Image Extensions installed to render WebP inline, and even then handled it inconsistently in older builds.

The complication is on the sending side. If you paste a WebP image into a New Outlook message and the recipient is using Classic Outlook, an older email client, or any reader that doesn’t have WebP decoding, they’ll see a broken image. The image is still in the email — the encoding is fine — they just can’t decode it. For external recipients, if you’re not sure what client they use, convert to JPEG or PNG before sending. The simplest path is to open the WebP in Paint, then Save as in your chosen format.

For internal email between modern Outlook clients (New Outlook, Outlook on the Web, current Outlook for Mac), WebP is reliable.

AVIF

AVIF is a more difficult case. The format is excellent technically — better compression than WebP, support for HDR, increasingly common on the web — but its support in Microsoft products lags significantly.

For viewing AVIF on Windows, you need the AV1 Video Extension from the Microsoft Store. With it installed, AVIF files render in Photos, File Explorer thumbnails, and — relevantly here — in New Outlook’s WebView2 renderer. Without it, you get the broken-image placeholder again.

For inserting AVIF into a New Outlook message, the situation is workable but not pretty. Pasted AVIF generally goes inline correctly if the codec is installed. Dragged AVIF from File Explorer follows the same drag-and-drop rules as any other image (see our drag-and-drop behaviour guide) and lands inline if dropped into the body.

The Microsoft Office desktop apps — Word, Excel, PowerPoint — do not natively support AVIF in 2026, and Microsoft’s own Q&A pages recommend converting to PNG or JPG before inserting. This is worth knowing because if you’re copying content from Word into a New Outlook message, AVIF images in the source document may or may not survive the round-trip in usable form.

The recommendation for AVIF in email is the same as it has been since the format launched: it’s great for your website, it’s not yet ready for general professional email. If you’re going to send images to people, convert them to JPEG, PNG, or WebP. Save the AVIF for places where you control the rendering stack.

JPEG XL

JPEG XL is the newest format in this list. Apple adopted it as a capture format on the iPhone 16 lineup, which means there’s now a population of iPhone users sending each other JPEG XL photos who don’t necessarily know they’re doing it.

On Windows, JPEG XL needs the JPEG XL Image Extension from the Microsoft Store. With it installed, JPEG XL files render inline in New Outlook the way other modern formats do. Without it, the format is unknown and produces a broken image.

The realistic expectation in 2026 is that JPEG XL support in your recipients’ email clients is sparse. Apple Mail handles it. New Outlook with the extension installed handles it. Most other clients don’t. If you’re forwarding iPhone 16 photos to a mixed audience, convert to JPEG first.

RAW formats and TIFF

For completeness, two format classes worth mentioning briefly.

Camera RAW files (Canon CR2, CR3, Nikon NEF, Sony ARW, and dozens of others) require the Raw Image Extension from the Microsoft Store to render thumbnails or previews anywhere on Windows. New Outlook can attach RAW files, but inline display is unreliable — and you almost never want a 40MB RAW file inline in an email anyway. Convert to JPEG for sending.

TIFF is handled by New Outlook’s WebView2 renderer with reasonable consistency. Multi-page TIFFs (common in scanning and faxing workflows) typically render only the first page inline. If your recipients need all pages, attach the file rather than embedding it inline.

Conversion paths worth knowing

If you’re going to be converting images often, the friction matters. A few options that work well for the New Outlook user.

The fastest path on Windows is Paint. Open any image format Windows knows how to decode, then File → Save as and choose JPEG or PNG. This handles HEIC, WebP, AVIF, and TIFF without ceremony, assuming you have the relevant codec extensions installed for the source format. For one-off images, this is hard to beat.

For batch conversion, the Photos app’s Edit and Create menu has a basic export option, but it’s slow and clunky for large numbers of files. A more reliable batch path is to install IrfanView or XnConvert — both are free, both handle every format in this article, and both let you convert hundreds of images in one operation.

OneDrive has a quietly useful behaviour worth knowing about: when you upload HEIC files from an iPhone via the OneDrive mobile app, you can configure it to auto-convert to JPEG on upload. In OneDrive Settings → Camera Upload → HEIC photos, choose Upload as JPEG. This eliminates the format problem at the source for anyone whose photo workflow involves OneDrive sync.

The default recommendation

If you take one thing from this article, take this: the safe formats for professional email in 2026 are still JPEG and PNG. They render everywhere, on every client, without anyone needing to install anything. Modern formats — HEIC, AVIF, WebP, JPEG XL — work in New Outlook when the right extensions are installed, but you have no visibility into what your recipients have installed, and there is no way to be sure they’ll see what you sent unless you convert.

When you’re sending images to people inside your organisation, on managed Windows fleets where IT has standardised the codec extensions, modern formats are fine. When you’re sending to external recipients — clients, prospects, anyone outside your tenant — convert to JPEG or PNG and stop worrying.

For the broader format compatibility picture across all Microsoft tools, our HEIC on Windows 11 complete guide covers the consumer side in depth, and the Microsoft Office image regression timeline tracks format-related bugs as Microsoft introduces and fixes them. For how New Outlook differs from Classic Outlook across the whole image-handling surface — not just formats — see our New Outlook vs Classic Outlook image handling guide.