The core difference is that Outlook Classic (desktop) uses the Microsoft Word rendering engine, which has historically very limited and outdated HTML/CSS support. New Outlook uses a modern Chromium-based rendering engine that supports more modern web standards.

Emails built for modern clients often break in Classic but look correct in New Outlook.

Common issues

Here are some issues that can arise when comparing the two:

• Table alignment, spacing and column widths can often render differently between the two
• Background images might not render in Classic
• Classic can ignore or alter margins, line-height and padding
• Media queries can be ignored in Classic, which is important in enabling true mobile responsiveness

Rendering inconsistencies

Key takeaways

• Use Outlook Classic as the lowest common denominator when creating HTML emails
• Use table-based layouts
• Use inline CSS
• Add fallbacks for background images and spacing
• Then enhance for modern clients (including New Outlook)

This mainly applies to HTML emails developed externally and pasted into the activity editor via an HTML block. Emails created with Taguchi's drag and drop activity editor have been tested for support in the following email clients.

Contact Taguchi support if you have any questions or need to raise an issue.