Real package inputHTML and local assets together
HTML email validator for macOS
Inspect the campaign.
Catch the defect before upload.
Open a real HTML email package, check its assets, links, markup and deterministic accessibility evidence, then export a preflight receipt without turning the app into a sending platform.
Native for MacmacOS 14+Apple notarization before launch
Native Release buildREAL APP
Explainable rulesEvery finding points to source
No sendingPreflight stays separate from delivery
One-time price$29 for one Mac, no subscription
Inside the actual app
The package stays reproducible.
The native app keeps the real asset and link inventory on the left, an actual WebKit viewport preview in the center and every source-backed blocker or warning on the right. Client parity is never implied.
Built for the real handoff
One focused app.
Four jobs done.
Email developers
Catch a broken asset or unsupported construct before the package enters a sending platform.
Marketing teams
Review links, unsubscribe placeholders and common viewport widths before scheduling.
Agencies
Export a source-backed receipt for a client handoff without uploading campaign files.
Template QA
Run the same deterministic checklist across recurring campaign packages.
The result
preflight-report.htmlpreflight-report.mdpreflight-report.jsonMANIFEST.sha256Private by defaultA clear workflow
From first record
to finished handoff.
Open the campaign
Choose an HTML file or package folder and inventory the actual images, fonts, attachments, links and placeholders.
Inspect and preview
Review email-safe HTML and CSS constraints, deterministic accessibility findings and the layout at 375, 600 and 800 pixels.
Verify links and export
Run the optional remote-link check, fix source-backed issues and export HTML, Markdown and JSON receipts with a checksum manifest.
Focused by design
Useful depth.
No account clutter.
HTML email rule checks
Catch external stylesheets, unsupported interactive elements, imported CSS and layouts that need fallback.
Asset inventory
Resolve local images, remote images, fonts and attachment references against the chosen campaign package.
Link and placeholder evidence
Check HTTPS use, remote response status, unsubscribe destinations and malformed merge placeholders.
Deterministic accessibility
Surface missing accessible names, document language, skipped headings and inline color contrast where the source proves it.
Honest viewport preview
Inspect common widths in native WebKit while keeping the difference between layout evidence and inbox-client parity visible.
Practical guides
Start with the job
you need to finish.
Questions, answered
MailPreflight FAQ
What does MailPreflight check in an HTML email package?+
It inventories local and remote assets, links, unsubscribe placeholders and email-specific HTML or CSS constraints, then adds deterministic language, heading, accessible-name and inline contrast findings.
Does it show how the email looks in every inbox?+
No. The 375, 600 and 800 pixel previews are layout evidence, not Gmail, Outlook or Apple Mail parity. Use your sending platform or a specialist rendering service for client-specific screenshots.
Can it check remote links?+
Yes, when you explicitly run the remote-link check. That is the one network action in the current core flow; opening and scanning the package itself remains local.
Does MailPreflight send email or manage a list?+
No. It does not send campaigns, store subscribers, calculate a spam score or claim deliverability.
Can it open a whole campaign folder?+
Yes. Open an HTML file or folder and MailPreflight resolves its local images, fonts and attachment references against the real package.
Does my campaign upload anywhere?+
No. Package parsing and viewport preview run locally. Only the optional remote-link check contacts the URLs you ask it to verify.
How much will MailPreflight cost?+
The price is US$29 as a one-time purchase for one Mac, with no subscription. Secure checkout and DMG delivery are handled by Polar.
MailPreflight for macOS
Inspect the campaign.
Catch the defect before upload.
A private Mac preflight desk for people who build HTML email and want deterministic defects out of the package before upload.
- macOS 14+
- One Mac
- Launch updates included
One-time purchase$29No recurring charge
Signed with Developer ID and notarized by Apple.