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How to Fix CSS Flexbox Collapse in iOS Mail (Apple)
for HubSpot Campaigns

A programmatic integration guide for resolving email rendering crashes inside iOS Mail (Apple) using HubSpot's layout editor environment.

Root Bug Analysis

iOS Mail (Apple) uses the WebKit Mobile which lacks support for standard rendering rules. This causes CSS Flexbox Collapse elements to break or collapse when rendering templates.

Active rendering engine: WebKit Mobile

HubSpot Specific Guide

HubSpot's delivery wrapper can clean and restructure elements during import, creating dynamic spacing differences inside iOS Mail (Apple).

Integration Step:

In HubSpot's Design Manager, edit the modules section. Create a 'Rich Text' or 'HTML' module block. Double-click the block, choose 'Tools' or 'Advanced', click 'Source Code', and drop the code snippet inside.

ESP Unsubscribe Alignment

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

HubSpot Unsubscribe Tag:{{ unsubscribe_link }}

Documented Client Behavior

Expected layout behavior based on target rendering engine specifications:

Documented behavior: CSS Flexbox Collapse causes elements to stack vertically or clip in iOS Mail (Apple) when templates are sent from HubSpot.

Interactive HubSpot Custom Sandbox

Target Environment: iOS Mail (Apple)

Auto-compile fixes inside RenderOps Workspace

Load layout code directly into our Retrofit Compiler to compile responsive table frameworks that display cleanly in iOS Mail (Apple).

Launch Retrofit Compiler

Fix CSS Flexbox Collapse on Other clients for HubSpot