Back to Toolkit
Google Search Verified Fix

How to Fix CSS Flexbox Collapse in Outlook 2013
for Mailchimp Campaigns

A programmatic integration guide for resolving email rendering crashes inside Outlook 2013 using Mailchimp's layout editor environment.

Root Bug Analysis

Outlook 2013's MSO parser treats flexible wrapper columns as raw paragraphs. Without nested table constraints, columns collapse and text overlaps.

Active rendering engine: Microsoft Word (MSO)

Mailchimp Specific Guide

Mailchimp's classic template pre-inliner injects reset sheets and wraps sections in 'mc:edit' tags, stripping head-level media conditional overrides on import. The fallback table structures must have absolute styles inlined directly.

Integration Step:

Locate your campaign block inside Mailchimp. Drag a 'Code' block into your canvas workspace. Toggle the editor view to Source, paste the optimized code, and click Save.

ESP Unsubscribe Alignment

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

Mailchimp Unsubscribe Tag:*|UNSUB|*

Documented Client Behavior

Expected layout behavior based on target rendering engine specifications:

Documented behavior: Mailchimp pre-inlining process strips head style blocks on import. Custom structures require explicit inline widths on table cells to prevent Outlook stacking.

Interactive Mailchimp Custom Sandbox

Target Environment: Outlook 2013

Auto-compile fixes inside RenderOps Workspace

Load layout code directly into our Retrofit Compiler to compile responsive table frameworks that display cleanly in Outlook 2013.

Launch Retrofit Compiler

Fix CSS Flexbox Collapse on Other clients for Mailchimp