In this article we will discuss some of our most frequently asked questions for rendering problems in Outlook. If you notice an issue that sounds similar to what you are running into, try the suggested fixes below to see if this resolves the issue. If the issue still persists after following the troubleshooting steps, reach out to our Knak Support team and we'd be happy to provide further guidance.
Background Turns Into Image When Forwarding
Outlook Classic for Windows converts background sections into images when forwarded.
This behavior cannot be changed.
Recommended workaround:
Enable Non-VML backgrounds (contact support)
Use a background color instead of an image
This keeps:
Text selectable
Links clickable
Full-Width Backgrounds Become Narrow
Outlook removes 100% width upon forwarding. This causes backgrounds to appear narrow.
Fix options:
Disable Full width background in Knak
Enable Non-VML backgrounds
Border Width Limit
Outlook only supports borders up to 8px.
Why this happens:
Outlook uses Microsoft Word rendering
Word limits borders to 6pt (≈ 8px)
Best practice:
Keep borders at 8px or less
Border Radius Not Working on Images
Outlook ignores rounded corners on images.
Reliable Fix:
Use PNG images with rounded corners built in
Learn more through this external source: https://www.caniemail.com/search/?s=border-radius.
Buttons Appear Square in Outlook
Outlook uses Vector Markup Language (VML) to render buttons with rounded corners.
VML is a Microsoft-specific coding method that helps ensure buttons display consistently in Outlook desktop apps.
In Knak, buttons are built using two versions:
A standard HTML version for most email clients
A VML version specifically for Outlook
If the VML version is removed or disabled, Outlook falls back to the HTML version.
This results in square corners instead of rounded corners.
When VML Is Disabled
VML may be disabled in the following scenarios:
Background images are applied to a section
Background images also rely on VML
Outlook does not support stacking multiple VML elements
Button VML is removed to prioritize the background
Your Email Service Provider (ESP) does not support VML tracking
Some platforms modify or strip VML code
Common examples include:
Eloqua
Adobe Campaign
SAP Marketing Cloud
SendGrid
SparkPost
Tracking or link rewriting conflicts occur
VML adds an extra clickable layer
This can interfere with click tracking in some platforms
VML has been manually disabled in your Knak account
This is sometimes done to simplify code
This removes rounded corners in Outlook permanently
What Happens When VML Is Disabled
Buttons display with square corners in Outlook
Only the text inside the button is clickable in some cases
Visual consistency across email clients is reduced
Recommended Solutions
Choose the option that best fits your use case:
Enable Non-VML Backgrounds
Allows VML buttons to function properly
Background images will not display in Outlook
A fallback background color will appear instead
Avoid using background images behind buttons
Prevents VML conflicts
Keeps rounded corners intact
Use non-VML buttons (if needed)
Improves compatibility with some ESPs
Removes rounded corners in Outlook
If you request to use non VML buttons for your account, corners of your buttons will always be square and only the link of the email itself will be clickable.
Need help updating your account settings?
Contact Knak Support to enable or disable VML features. This helps ensure your buttons render correctly in Outlook.
Button Not Showing in Outlook
Outlook may hide buttons without valid links.
Fix:
Add a full link (include
https://)Sync tokens with your Marketing Automation Platform (MAP)
Button Text Is Cut Off
Outlook does not support custom web fonts. Fallback fonts can change button size.
Fix steps:
Use a similar fallback font
Increase button padding or width
Use web-safe fonts
Use whole-number line height (1, 2, etc.)
Center-align text
Consider non-VML buttons
Button Not Fully Clickable When Forwarded
Forwarding removes styles and breaks VML.
Fix options:
Use Forward to a Friend links
Enable HTML optimized for forwarding (contact Knak support)
Use non-VML buttons
Custom Bullet List Styles
Image Bullets Not Supported in Nested Lists
Outlook does not support image-based bullets in nested lists. A nested list is a list inside another list, used to group related items under a main point.
Example:
Main item
Sub item
Sub item
When image bullets are used in this structure, Outlook replaces them with default bullet styles.
This means:
Custom bullet designs will not display as intended
Nested items will fall back to standard bullets
Formatting may appear differently compared to other email clients
Recommendation:
Avoid using image bullets in nested lists
Use standard bullet styles for better consistency
Keep list formatting simple to reduce rendering issues
Extra Spacing in Bullet Lists
Outlook may add small spacing differences (1–2px) between bullet points. This is caused by differences in how fonts and line spacing are rendered in Outlook.
This means:
Spacing may appear slightly larger than in other email clients
Indentation and alignment may not match exactly
Small inconsistencies can vary by device and Outlook version
This behavior cannot be fully controlled.
Recommendation:
Allow for slight spacing variations in your design
Avoid relying on pixel-perfect alignment for bullet lists
Test across email clients to ensure acceptable rendering
Dark Mode Edits Not Applied
Outlook does not support dark mode editing.
Since Outlook does not support dark mode editing, here are some articles that discuss best practice tips to mitigate these issues:
Color changes: Color Choices for Dark Mode and Color Contrast for Dark Mode
Utilizing borders: Borders and Dark Mode and Using Borders on Buttons in Dark Mode
Expand this section to view a chart displaying the default behavior for color changes that display for Outlook emails
Expand this section to view a chart displaying the default behavior for color changes that display for Outlook emails
Email Client | Default Behavior in Dark Mode |
Apple Mail (iPhone & iPad) | May darken some elements, particularly white backgrounds |
Apple Mail (Mac) | May darken some elements, particularly white backgrounds |
Outlook (Mac - latest version) | Darkens bright colors and backgrounds, lightens text |
Outlook (Mac - older versions) | Darkens bright colors and backgrounds, lightens text |
Outlook (Windows 365 & 2021+) | Inverts all colors (white becomes black, black becomes white) |
Outlook App (Android) | Darkens bright colors and backgrounds, lightens text |
Outlook App (iOS) | Darkens bright colors and backgrounds, lightens text |
http://Outlook.com (Browser) | Darkens bright colors and backgrounds, lightens text |
Gmail App (iOS) | Inverts all colors (white becomes black, black becomes white) |
Gmail App (Android) | Darkens bright colors and backgrounds, lightens text |
Yahoo App (iOS) | Darkens bright colors and backgrounds, lightens text |
Yahoo App (Android) | Darkens bright colors and backgrounds, lightens text |
And for further assistance, check out this video for an overall crash course on best practices for dark mode editing:
Can You Override Dark Mode Styles?
Knak applies built-in fixes to improve how emails render in Outlook Dark Mode.
These fixes help maintain readability, but control is limited.
What Knak does automatically:
Applies Microsoft Office (MSO) gradient text fixes for buttons
Preserves text visibility with fallback colors
Improves color contrast where possible
Important limitations:
Outlook does not support true dark mode targeting
Media queries and custom dark mode styles are ignored
Outlook may override your colors automatically
Rendering can vary by version:
Some versions invert background colors
Some adjust text only
Some ignore styling completely
Best practices:
Use high-contrast colors
Avoid text over complex background images
Add borders to buttons and sections
Use transparent images when possible
Test across multiple Outlook versions
Fonts Look Different in Outlook
Outlook does not support custom web fonts.
What happens:
Outlook uses fallback fonts instead
Tip:
Choose fallback fonts close to your brand style
Text Automatically Turns Into Links
Outlook may auto-link:
Phone numbers
Addresses
Fix:
Add links manually using Knak
Long Links Do Not Wrap
Outlook does not handle long text or URLs well.
Fix options:
Use buttons instead of long links
Shorten display text
Add spacing to break long text
External Sender Banner Alters Emails
Security tools may modify incoming emails before they reach your inbox.
This is common in many business-to-business (B2B) environments.
Common banner:
“External sender” warning
These tools intercept and scan emails for security risks. During this process, they may:
Rewrite parts of the HTML
Add tracking or scanning code
Inject banners or additional elements into the email
This can affect rendering by:
Shifting layout or spacing
Breaking styles or formatting
Causing elements to appear differently than expected
Important:
These changes happen outside of Knak
The behavior varies by organization and security provider
The same email may render differently across recipients
Recommended solution:
Ask your IT team to add the sender to your Safe Senders list
This prevents the email from being modified
Unsubscribe Link Looks Broken in Outlook.com
Outlook.com modifies unknown tokens like {{Unsubscribe}}.
What to expect:
Displays both link and text
Fix:
Send through your MAP so tokens resolve
White Lines in Outlook Emails
Outlook converts pixels to points. This causes rendering gaps.
Important:
Cannot be fully fixed
Only minimized
Tip:
Review this guide for best practice tips to mitigate the issue: https://help.knak.io/en/articles/9421305-outlook-issue-white-lines
Note: Microsoft is releasing a completely overhauled version of Outlook over the next few years (which uses the Outlook.com rendering under the hood) which will completely remove this issue.
Need more help? Contact support via live chat within Knak using the chat bubble in the bottom right corner or email support@knak.com