Broken rendering and inaccessible layouts lower engagement and, in some jurisdictions, create legal exposure.
The metrics that matter#
- Authentication pass rate: share of mail passing SPF, DKIM, and DMARC alignment. Healthy: 99% or higher.
- Spam complaint rate: Gmail enforces at 0.3%; stay under 0.1%.
- Hard bounce rate: under 2%; above 5% triggers platform reviews.
- Inbox placement: above 90% across major providers via seed tests.
- Engagement: click and reply rates by segment; opens are unreliable after Mail Privacy Protection.
Where to read them#
- Google Postmaster Tools for Gmail domain reputation, spam rate, and authentication.
- Microsoft SNDS and JMRP for Outlook.com IP reputation and complaints.
- Your ESP's delivery and bounce reports.
- DMARC aggregate reports for authentication by source.
Improving the numbers#
- Use a single-column layout that reflows on mobile.
- Set alt text on every meaningful image and empty alt on decorative ones.
- Maintain 4.5:1 contrast and at least 16px body text.
- Include a plain-text alternative and test in dark mode.
Frequently asked questions#
Does dark mode change email colors?
Some clients invert or adjust colors. Test in Gmail, Outlook, and Apple Mail dark modes and use transparent PNGs where possible.