Background images in Classic Outlook email signatures
A CSS background can look correct in a browser and still require special treatment in Classic Outlook. This matters when a signature relies on a background for essential branding or readable content.
What Microsoft documents
Microsoft’s current email-rendering guidance says Classic Outlook does not natively support CSS background images on sections and columns. Microsoft documents VML as the compatibility technique used when a background image must be supported in Classic Outlook.
What SigLint flags
<td style="background-image:url('brand-bg.png')">…</td>SigLint reports CSS background or background-image values that contain a URL and labels the finding for Classic Outlook.
Safer direction for signatures
If the image is essential—such as a logo—prefer a normal <img> element with explicit dimensions. If a true background is essential, use a tested Outlook-specific implementation and verify it in the real Classic Outlook clients you support.