How Buttons Work in Knak
Knak uses a coding technique called Vector Markup Language (VML) buttons. Vector Markup Language is Microsoft’s markup language used for styling shapes in Outlook.
VML ensures that buttons display correctly across many email clients.
The system creates two versions of each button:
A VML version for Outlook desktop clients.
A standard HTML version for all other email clients.
The Outlook version uses conditional comments. These comments apply special code only for Outlook. This approach improves visual consistency across platforms.
Knak Button Options
Knak offers two button types.
VML Buttons (Default)
VML buttons are the default option in Knak.
Benefits
Consistent appearance across most email clients
Rounded corners render correctly
The entire button area is clickable
Choose this option when visual consistency across email clients is the priority.
Non-VML Buttons (Alternative)
Non-VML buttons remove the Outlook-specific VML code.
Benefits
Click tracking works in platforms such as Eloqua
Button appearance remains consistent across most clients
Trade-offs
In Outlook 2007–2013:
Button corners appear square
Only the text link is clickable instead of the full button
Tracking Limitations With Some Email Service Providers
Some Email Service Providers (ESPs) do not support tracking links inside Vector Markup Language (VML) code.
If your ESP does not support VML tracking, clicks may not be recorded in your reports.
Common ESPs Affected
This limitation has been observed in platforms such as:
Eloqua
Adobe Campaign
SAP Marketing Cloud
SendGrid
SparkPost
In these cases, we recommend using non VML buttons instead. Reach out to Knak Support if you need non VML buttons enabled.
Known Limitation With VML and Background Images
Microsoft Outlook has a technical limitation. Outlook does not support two layers of Vector Markup Language (VML) within the same section of an email.
Knak uses VML for two features:
Buttons
Background images
If a VML button is placed inside a section that uses a background image, Outlook cannot render both VML elements correctly.
VML Buttons With VML background images:
What This Means
You may notice the following behavior in Outlook desktop clients:
The button may not render correctly
The button may lose styling
The background image may not display as expected
This issue occurs in Outlook desktop versions that use the Microsoft Word rendering engine.
How to Avoid This Issue
Use one of the following approaches.
Option 1: Enable Non-VML Buttons
Contact Knak Support to enable non-VML buttons for your account.
This removes the layered VML issue. Buttons can render correctly in sections with background images.
Non-VML buttons (with VML Background Images)
Option 2: Enable Non-VML Background Images
As an alternative, Knak Support can enable non-VML background images for your account.
This allows you to continue using VML buttons without encountering the layered VML issue.
However, this change affects all background images across your account.
Background images will not render in Outlook desktop clients
Outlook will display the fallback background color
Background images will still render correctly in other email clients
Choose this option when button styling is more important than background images in Outlook.
VML Buttons (with Non-VML Background Images)
Need more help? Contact support via live chat using the chat bubble in the bottom right corner or email support@knak.com.