Fix Custom Font Fallback Overrides in Mozilla Thunderbird — MJML Framework Guide for B2B Cold Outreach
B2B cold outreach templates demand maximum deliverability and a plain-text appearance. Heavy, broken CSS structures or HTML syntax issues trigger spam filters instantly. Below is the targeted integration guide to fix Custom Font Fallback Overrides inside Mozilla Thunderbird templates when using MJML Framework.
Technical Breakdown
Mozilla Thunderbird uses the Gecko which lacks support for standard rendering rules. This causes Custom Font Fallback Overrides elements to break or collapse when rendering templates.
MJML Framework Behaviors
The MJML transpilation compiler parses dynamic columns and wraps them in custom HTML conditional tags. If you paste direct tables or VML code blocks inside an MJML layout without proper escaping, the MJML compiler will try to clean the code, resulting in stripped Outlook namespaces and broken layouts. For cold sales outreach, minimize VML structures and prioritize light, standard text blocks to maximize inbox placement on corporate enterprise filters.
Remediation Code Block
To prevent Outlook's Times New Roman fallback override, wrap your custom font declarations inside an @media block that Outlook ignores, or use MSO conditional statements to override font-families specifically for Microsoft Word rendering engines. In your MJML Framework campaign manager, make sure you configure your links to run via {{unsubscribe_link}}.
<!--[if mso]>
<style type="text/css">
body, table, td { font-family: Arial, sans-serif !important; }
</style>
<![endif]-->
<style>
@import url('https://fonts.googleapis.com/css2?family=Montserrat&display=swap');
</style>Live Code Sandbox Test
How to Deploy inside MJML Framework
Copy the fixed VML or table wrapper code block from the remediation box above.
Wrap the entire RenderOps corrected table block inside an '<mj-raw>' tag block. This tells the MJML compiler to bypass parsing on this segment, exporting the exact conditional statements into the final HTML output.