What Most People Miss About Outlook and WebP Support

You paste a crisp WebP chart into an email. Hit Send. Recipient replies: 'I see a broken image icon.' You check their Outlook — same thing. You try again from your phone. Still broken. No error message. No warning. Just silence and disappointment.

Quick Answer

No, Outlook desktop (365, 2021, 2019, 2016) and Outlook on the web (OWA) do not render WebP images inline in emails. They block them silently or show a placeholder. To confirm: open any email with a WebP attachment or embedded WebP, then right-click > Properties — you’ll see the file type listed but no preview. There is no toggle or setting to enable WebP under File > Options > Mail > Compose messages or anywhere else.

Step-by-Step Walkthrough

Test it yourself: Drag a .webp file into a new email (Ctrl+N). Don’t paste — drag. Outlook accepts it as an attachment but won’t render it inline — even if you double-click the thumbnail.
Check rendering behavior: Send that email to yourself. Open it in Outlook desktop (not OWA yet). Right-click the attachment > Save As, then open the saved file in Windows Photos — it’ll display fine. But inside Outlook? Blank box or red X.
Try Outlook on the web: Log into office.alibaba.com > Outlook. Compose a new message. Paste a WebP image directly (Ctrl+V). It converts to PNG automatically — but only if pasted *into the body*. If dragged in as an attachment? Still blocked. No warning. Just invisible.
Verify Exchange server impact: Go to File > Account Settings > Account Settings… > select your account > Change > More Settings > Advanced. Look for “Use Cached Exchange Mode” — enabled or not, WebP still fails. The limitation lives in Outlook’s HTML rendering engine (Word-based), not Exchange. So no admin policy fixes this.

Common Pitfalls

Assuming WebP works because it’s in your browser: Chrome and Edge handle WebP natively — but Outlook uses Word’s rendering engine (same one that powers .docx), which hasn’t added WebP support since 2012. That hasn’t changed in Outlook 365 v2405 or 2407.
Dragging WebP into signature editors: Some users drop WebP into File > Options > Mail > Signatures > Edit signature. It appears during editing, then vanishes when sent. No error. Just gone.
Using "Insert > Pictures" and selecting WebP: Outlook lets you browse and pick it — then inserts a blank line or broken icon. It doesn’t reject the file; it pretends to accept it.
Thinking OWA is safer: Outlook on the web strips WebP from pasted content and silently substitutes PNG — but only for inline paste. Attachments remain WebP and unviewable. So recipients get either nothing or a surprise format shift.

Pro Tips

Most people convert WebP manually before emailing. Power users skip that step entirely.

Auto-convert on paste (desktop only): Install the free WebPtoPNG Outlook add-in. It intercepts paste events and swaps WebP for PNG before insertion. Works in Outlook 365 (v2312+) and 2021. No restart needed — just enable under File > Options > Add-ins > COM Add-ins > Go….
Keyboard shortcut workaround: Ctrl+Alt+V opens Paste Special. Choose “Bitmap Image” — Outlook forces conversion to BMP, which displays. Not ideal quality-wise, but guaranteed to appear. Try it with a 100KB WebP chart — becomes ~800KB BMP, but visible.
Use SVG instead (for charts & icons): Outlook desktop supports SVG inline — but only if embedded as HTML <img src="data:image/svg+xml;base64,...">. Not drag-and-drop. Requires editing HTML source (Alt+F9 to toggle field codes, then paste raw SVG base64). Rarely used, but bulletproof for vector graphics.

Troubleshooting

If you swear you saw WebP work once — it was probably cached, misidentified, or a false positive. Here’s why it fails, and why “fixes” don’t stick:

Version lock-in: Outlook 365 (monthly channel) added limited WebP support to file attachments view in build 2406 — but only in the attachment pane, not inline. You’ll see the filename and icon, but clicking opens it externally. Desktop Outlook 2019 and earlier? Zero support anywhere.
Admin restrictions don’t apply — but they could make it worse: Group Policy settings like “Block unsafe file types” won’t list WebP (it’s not blocked by default), but if admins add .webp to the prohibited list, Outlook will reject it outright — no attachment, no warning, just silent failure.
Exchange Online doesn’t process WebP: Even if you bypass Outlook and send via Graph API with WebP embedded in base64, Exchange strips it or renders as blank. Confirmed across E3, E5, and Microsoft 365 Business Standard tenants.
Mobile Outlook apps ignore WebP completely: iOS and Android clients don’t render, preview, or warn. Attachment shows up in list, but tapping does nothing — no “unsupported format” alert, just freeze or back-out.

Bottom line: WebP is unsupported, undocumented, and unfixable at the Outlook layer. Microsoft has never announced plans to add it — and Word’s rendering engine remains the bottleneck.

Setting Name	Location	Options	Recommendation
Inline image rendering engine	Built into Word HTML renderer (not configurable)	JPEG, PNG, GIF, BMP only	Convert WebP to PNG before inserting
Attachment preview behavior	File > Options > Trust Center > Trust Center Settings > Attachment Handling	“Show preview for known file types”, “Block unknown types”	WebP is “unknown” — disable preview to avoid confusion
HTML paste handling (OWA)	Server-side (no client control)	PNG fallback only for direct paste	Always paste charts as PNG — never rely on auto-conversion
Signature image format	File > Options > Mail > Signatures	Supports PNG, JPEG, GIF only	Save WebP as PNG first, then insert
Cached Exchange Mode effect	File > Account Settings > Account Settings > Change > More Settings > Advanced	On / Off	No impact — WebP fails regardless