Definition
Outlook for Windows renders email using Microsoft Word's HTML engine — not a standard browser engine — which means standard CSS often does not work. mso conditionals are special HTML comments that only Outlook processes, allowing you to apply Outlook-specific fixes.
Common mso Properties
mso-line-height-rule: exactly— Prevents Outlook from adding extra line spacingmso-hide: all— Hides elements from Outlook (useful for progressive enhancement)mso-table-lspaceandmso-table-rspace— Removes table cell spacing in Outlookmso-padding-alt— Sets padding specifically for Outlook
Example
<!--[if mso]>
<td style="padding: 20px;">This only renders in Outlook</td>
<![endif]-->
Why It Matters
Outlook for Windows still holds significant market share in B2B environments. Without mso-specific fixes, emails can break or look unprofessional for a substantial portion of your B2B audience.
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