Why is 600px the standard width for HTML emails?

Most desktop email clients (especially Microsoft Outlook on Windows) feature a reading pane with fixed width constraints. A 600px container guarantees that emails display without horizontal scrollbars.

Why does Microsoft Outlook break CSS Grid and Flexbox?

Outlook for Windows uses the Microsoft Word rendering engine (Word HTML), which does not support CSS flexbox, grid, or float layout models. Table-based layouts ( , , ) remain mandatory for reliable cross-client email rendering.

HTML Email Client Previewer & Compatibility Auditor

Simulate HTML emails across Desktop (600px), Tablet (768px), and Mobile (375px) viewports. Audit for Outlook/Gmail rendering quirks, unsupported CSS, and missing preheaders offline.

Viewport Desktop (600px)

Outlook Compatibility EXCELLENT

Warnings 0

Preheader Text Detected

HTML EMAIL CODE & CSS AUDIT 0 lines

CLIENT RENDERING VIEWPORT 600px × 600px

Frequently Asked Questions

What is email preheader text?

Preheader text is the preview snippet displayed next to or below the subject line in modern inboxes (Gmail, Apple Mail, Outlook). Adding a hidden <span style="display:none;font-size:1px;max-height:0px..."> element controls this snippet without cluttering the email body.

Why should images always have explicit width and height?

When email clients initially block images, missing width and height attributes cause the entire table layout to collapse, destroying the visual hierarchy.