Overview
Microsoft Outlook for Windows limits how borders display in emails.
Knak prevents this issue by enforcing a maximum border width for emails. This ensures your designs render consistently across email clients.
Border Width Limitation in Outlook
Outlook for Windows only supports borders up to 8 pixels (px) wide.
Any border larger than 8px renders as 8px
This happens during email rendering, not during design
The limitation cannot be overridden with code or settings
Why This Happens
Outlook uses the Microsoft Word rendering engine to display emails.
Microsoft Word limits borders to 6 points, which equals 8 pixels.
Because of this:
Outlook inherits the same restriction
Border widths are capped automatically
The same behavior appears in Microsoft Word documents
How Knak Handles This
Because of this behavior, Knak caps border widths at 8px for emails.
This helps ensure consistent rendering across email clients
Your design appears as expected in Outlook and other inboxes
You avoid unexpected visual changes after sending
Recommended Workarounds
Since this is a system limitation, use alternative design approaches.
Use Background Color Blocks
Replace thick borders with padded containers
Apply background color to simulate a border
Use Nested Tables
Create an outer container with background color
Add inner spacing to mimic border thickness
Keep Borders Thin
Design with 8px or less for consistent rendering
Test emails in Outlook early
Best Practices
Design for Outlook first if your audience uses it
Avoid relying on thick borders for key visuals
Use spacing and color instead of heavy outlines
Test across email clients before sending
Need more help? Contact support via live chat using the chat bubble in the bottom right corner or email support@knak.com.