If your mail server lands on a major DNSBL, deliverability collapses overnight. Use this guide to monitor your sending IPs and domains continuously, catch listings early, and recover before customers notice.
DNS-based blocklists are queried in real time by receivers when your server connects. A listing means most providers will reject or aggressively filter your messages, often without bouncing visibly to your end. Reputation is rebuilt slowly; protect it.
Run through these steps in order. Each step links to the right diagnostic tool.
Spamhaus (SBL, XBL, PBL), Barracuda, SORBS, and SpamCop. Microsoft and Google maintain internal lists too — those affect Outlook and Gmail respectively.
Some receivers reject immediately on Spamhaus listings. Others soft-fail and the impact grows over hours. Either way, recovery takes longer than damage.
Both. Sending IPs control SMTP-level acceptance; domains affect DKIM/DMARC reputation at the inbox provider.
Fix the root cause (spam complaints, compromised account, open relay), then submit a delisting request through the DNSBL's removal form.
Monitor it continuously
Save this check, get alerts on changes, and track multiple domains in one dashboard.