Complaints are the strongest negative signal. FBLs let you suppress complainers immediately and detect problem campaigns before reputation collapses.
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#
- Register your sending IPs and domains with each provider's FBL.
- Route FBL messages to an automated parser.
- Suppress every complainer from all future marketing.
- Report complaint rate per campaign and per acquisition source.
Frequently asked questions#
Does Gmail offer a feedback loop?
Only an aggregate one via Postmaster Tools using the Feedback-ID header. Gmail does not return individual complaints.