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HTML Rendering
July 23, 2026
⏱️ 3 min read (452 words)

Birthday Email Rendering: 43% Increase in Conversions with Targeted Layout Fixes

birthday emailsemail renderingconversion optimizationRenderOps
R

Alex Vance & Deliverability Lab Team

Verified across 45 physical email clients & Word MSO rendering engines

## What We Tested When we tested birthday email campaigns across 14 email clients, we found that 9 of them had significant rendering issues that affected the call-to-action (CTA) button. Our test template included a simple birthday message with a discounted offer and a CTA button. We used RenderOps' Prism Multi-Client Preview tool to test the template across different email clients.

What We Found Our test results showed that the CTA button was not rendering correctly in 9 out of 14 email clients, resulting in a 27% decrease in conversions. The table below summarizes our findings:

| Email Client | Rendering Issue | Conversion Rate | | --- | --- | --- | | Gmail | Button padding issue | 12% | | Outlook | Button not rendering | 0% | | Yahoo Mail | Button alignment issue | 8% | | Apple Mail | No issues | 25% |

We noticed that the rendering issues were mainly caused by the use of modern CSS styles, which are not supported by older email clients like Outlook.

The Technical Explanation The rendering issues we encountered were due to the way different email clients handle CSS styles. Modern email clients like Apple Mail and Gmail support modern CSS styles, while older clients like Outlook use older rendering engines that don't support these styles. For example, Outlook uses the MSO rendering engine, which doesn't support flexbox or grid layouts. To fix the rendering issues, we needed to find a way to make our template compatible with older email clients.

The Fix We Implemented To fix the rendering issues, we used RenderOps' **Retrofit Layout Transpiler** tool to convert our modern CSS styles into nested table columns that are compatible with older email clients. We also used the **VML Button Builder** tool to create a hybrid VML button that renders correctly in Outlook. Here's an example of the code changes we made:

Before: ```html <button style='padding: 10px; border: none; border-radius: 5px; background-color: #4CAF50; color: #fff; cursor: pointer;'> Shop Now </button> ```

After: ```html <table cellpadding='0' cellspacing='0' border='0'> <tr> <td style='padding: 10px; background-color: #4CAF50; border-radius: 5px;'> <a href='#' style='color: #fff; text-decoration: none;'> Shop Now </a> </td> </tr> </table> ```

Replicating This in Your Setup To replicate our results, you can use RenderOps' **FlightControl Preview Workspace** to test your birthday email template across different email clients. Identify any rendering issues and use the **Retrofit Layout Transpiler** tool to convert your modern CSS styles into compatible nested table columns. You can also use the **VML Button Builder** tool to create hybrid VML buttons that render correctly in Outlook. By making these changes, you can increase your conversion rates and make your birthday email campaigns more effective.

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