Blocklists
A sending IP or domain appears on a DNS blocklist used by receivers or downstream filters.
- Reading time:
- 5 min
- Difficulty:
- Advanced
- Estimated duration:
- 5 min
- Prerequisites:
- None
- Last updated:
- 2026-07-15
- Author:
- empire
Problem summary
A sending IP or domain appears on a DNS blocklist used by receivers or downstream filters.
Severity: Critical
Symptoms
- Blocklist query tools show a listing for IP or domain
- Sudden rejects citing blocked/listed senders
- Delivery collapses at multiple receivers at once
Possible causes
- Spamtrap hits or abuse complaints
- Compromised account or open relay behavior
- Neighbor damage on a shared IP
- Malware or form-injection sending spam
How to diagnose
- Confirm which list and whether IP or domain is listed
- Identify traffic that preceded the listing
- Check for account compromise or unexpected outbound volume
How to fix
- Stop abusive traffic immediately
- Follow the list’s delisting process with evidence of remediation
- Move clean traffic off burned shared infrastructure if needed
How to verify
- Listing cleared on authoritative lookup
- Rejects citing the list stop
Prevention
- Monitor major lists for sending IPs
- Enforce abuse detection on outbound systems
When to escalate
- Production mail is failing for a material share of recipients after remediation attempts
Related Learn Articles
- ReputationHow mailbox providers judge senders from IP, domain, and behavioral signals over time.
- DeliverabilityWhether mail is accepted and where it is placed — inbox, promotions, spam, or rejected.
- Spam trapsAddresses maintained to detect poor acquisition or stale lists; hits damage reputation quickly.
Related Problems
- Domain reputation degradedAuthenticated domain identity is treated as untrusted despite IP changes.
- Failed reputation recoveryRemediation attempts stall because harmful traffic or volume ramps continue.
- High bounce ratePermanent or repeated delivery failures indicate poor list quality and hurt reputation.
- High complaint rateSpam reports exceed provider expectations and are damaging IP or domain reputation.
- IP reputation degradedA sending IP is throttled, junked, or rejected due to accumulated negative signals.
- Missing reputation monitoringNo FBLs, postmaster views, or bounce classification are in place to detect damage early.
- Shared IP neighbor damagePoor practices from other senders on a shared IP are poisoning delivery outcomes.
- Spam trap hitsMail is reaching trap addresses, signaling acquisition or hygiene failures.