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Fix Gmail Line-Height Shifts in Mozilla Thunderbird — Brevo (Sendinblue) Guide

A programmatic integration guide for resolving email rendering crashes inside Mozilla Thunderbird using Brevo (Sendinblue)'s layout editor environment.

Root Bug Analysis

Mozilla Thunderbird uses the Gecko which lacks support for standard rendering rules. This causes Gmail Line-Height Shifts elements to break or collapse when rendering templates.

Active rendering engine: Gecko

Brevo (Sendinblue) Specific Guide

Brevo (Sendinblue)'s delivery wrapper can clean and restructure elements during import, creating dynamic spacing differences inside Mozilla Thunderbird.

Integration Step:

Open Brevo's template canvas, select the element you wish to configure, click 'Edit HTML' or insert a standalone 'HTML' content block, and paste the code.

ESP Unsubscribe Alignment

When compiling custom HTML templates for Brevo (Sendinblue), you must ensure your layout retains deliverability compliance loops. Brevo (Sendinblue) requires you to insert their specific unsubscribe merge tag, otherwise your campaign delivery will be flagged by automated spam audits.

Brevo (Sendinblue) Unsubscribe Tag:{{ unsubscribe }}

Documented Client Behavior

Expected layout behavior based on target rendering engine specifications:

Documented behavior: Gmail Line-Height Shifts causes elements to stack vertically or clip in Mozilla Thunderbird when templates are sent from Brevo (Sendinblue).

Interactive Brevo (Sendinblue) Custom Sandbox

Target Environment: Mozilla Thunderbird

Auto-compile fixes inside RenderOps Workspace

Load layout code directly into our CSS Inliner to compile responsive table frameworks that display cleanly in Mozilla Thunderbird.

Launch CSS Inliner

Fix Gmail Line-Height Shifts on Other clients for Brevo (Sendinblue)