The 12-Point HTML Email Testing Checklist

You can spend two hours crafting a beautiful HTML email and one minute breaking it in Outlook. Here is my personal 12-point testing checklist I run before every campaign — the same one baked into our Free HTML Email Preview tool.

The 12 checks that catch 95% of issues

Outlook is where dreams die

Outlook uses Word's HTML engine. It ignores 3-column flex layouts, half of CSS3, and animated GIFs beyond the first frame. Rule of thumb: nested tables + inline styles + max width 600px = you will survive.

html
<!-- Outlook-safe hero block -->
<table role="presentation" width="600" cellpadding="0" cellspacing="0" style="max-width:600px;margin:0 auto;">
  <tr>
    <td style="padding:32px;background:#0B996E;color:#fff;font-family:Arial,sans-serif;">
      <h1 style="margin:0;font-size:28px;">Welcome to Brevo</h1>
    </td>
  </tr>
</table>

Dark mode is not optional in 2025

Apple Mail dark mode auto-inverts light-only emails, often catastrophically (white logos on white backgrounds). Use CSS media queries and provide explicit dark variants of your logos and body colors.

Automate the boring checks

Our Free HTML Email Preview tool renders your HTML in a sandbox and lets you toggle between light/dark instantly. Use it for the first pass before hitting a paid tool like Litmus or Email on Acid for full inbox testing.