HTML email preflight guide
HTML email validator for Mac: preflight checklist
Email preflight is most useful before the campaign enters a sending platform. Keep the HTML and its local assets together, then make every reported defect reproducible from the source.
1. Open the complete package
Start with the HTML file and the folder that contains images, fonts and attachments. A browser preview alone will not reveal every missing local reference.
2. Run email-specific markup checks
Look for linked stylesheets, imported CSS, interactive elements and modern layouts that need a reliable fallback in inbox clients.
3. Inspect links and placeholders
Verify the unsubscribe destination, merge placeholders, protocol use and optional remote response status before scheduling the campaign.
4. Separate preview from client parity
Use common viewport widths to inspect layout evidence, then rely on the intended sending platform or a specialist service for client-specific rendering screenshots.