Why Does My Transparent Logo Show a White Background in Outlook Email Signatures?

A transparent logo shows a white background in an Outlook email signature because Outlook — especially in Dark Mode — adds its own solid fill behind transparent PNGs instead of preserving the alpha channel. The logo file itself is usually fine; Outlook's rendering engine is forcing the white box. You can fix it by placing the image inside an HTML table cell, using a logo with a colored or outlined mark that reads on any background, or confirming the file is a true transparent PNG (not a JPEG that baked in white).

Why Outlook Adds a White Background to Transparent Logos

• Outlook doesn't render PNG alpha transparency the way browsers do — its rendering engine (based on Word, on Windows) often substitutes a solid fill.
• In Dark Mode, Outlook deliberately places a white or light box behind transparent images so they stay visible against a dark background — which looks like a bug but is intentional.
• If the "transparent" logo was ever saved or exported as a JPEG, transparency was stripped and a real white background was baked in — that white is now part of the image.
• The same signature can look perfect while composing but show the white box after sending, because the sender and recipient clients render the image differently.

How to Fix the White Background

1. Confirm the file is truly transparent: Drag the logo into a browser tab — if it's see-through there but white in Outlook, the file is fine and the issue is Outlook's rendering.
2. Wrap the logo in a table cell: In your signature HTML, place the <img> inside a <table><tr><td> structure — this helps Outlook preserve transparency in Dark Mode.
3. Edit the signature file directly (Windows): Signatures live in C:\Users\<you>\AppData\Roaming\Microsoft\Signatures\ as .htm files — open and adjust the image markup there.
4. Use a Dark-Mode-safe logo: Choose a version with a colored or outlined mark (or a subtle glow/stroke) so it reads cleanly on both white and dark backgrounds.
5. Re-export as a real transparent PNG: If the white is baked into the file, remove the background again and export a true transparent PNG — never a JPEG.

Prepare Your Logo So It Never Boxes Out

• Always use PNG (or SVG where supported) for signature logos — JPEG cannot hold transparency and will always show a solid background.
• Keep a version of the logo with adequate contrast on dark backgrounds, since many recipients read email in Dark Mode.
• Test your signature by sending it to yourself and viewing it in Outlook desktop, Outlook web, and the mobile app — rendering differs across all three.
• Start from a clean, genuinely transparent cutout so the only variable left is Outlook's rendering, not the file.

EraserPro's background remover exports a true transparent PNG in seconds, so your logo starts clean before Outlook ever gets a chance to render it wrong.

Frequently Asked Questions