A Spamhaus SBL or DBL listing can block delivery to a large share of the internet within hours.
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#
- Check your IPs and domains against major blocklists weekly.
- Identify the cause: compromised account, list purchase, spam trap hits, or a misconfigured forwarder.
- Fix the root cause and document what changed.
- Submit a delisting request through the blocklist's process with evidence of remediation.
- Monitor for relisting for 30 days.
Frequently asked questions#
How long does Spamhaus delisting take?
Often within hours for SBL and CSS if the cause is fixed. DBL domain listings can take longer.
Which blocklists matter most?
Spamhaus (SBL, XBL, DBL), SpamCop, Barracuda, and SURBL have the widest impact.