DNS-based blocklists that flag IPs and domains known for sending spam — and how to get off them.
⚡ Monitored by EmailExacto IntelligenceEmail blacklists (DNSBLs) are real-time databases of IP addresses and domain names known for sending spam or malicious email. Mail servers query them on every delivery attempt to decide whether to accept, filter, or reject the message. A single listing on Spamhaus XBL or SBL can cause widespread delivery failure across the internet.
DNSBL lookups work by reversing IP octets and querying a specific zone. For IP 203.0.113.10 on Spamhaus ZEN:
Major lists include: Spamhaus ZEN (XBL+SBL+PBL combined), Barracuda BRBL, SORBS, SpamCop, URIBL, and Invaluement. Most large receivers query Spamhaus at minimum.
A blacklist listing can instantly cause email to bounce, land in spam, or be rejected at the gateway. The impact ranges from mild filtering to complete delivery failure. Listings occur from spam trap hits, high complaint rates, sending to invalid addresses, compromised accounts, or residential IP ranges.
EmailExacto checks your sending IPs and domain against 12 IP DNSBLs and 4 domain blocklists daily, with delist links in your daily report.
✓Monitor your sending IPs against major DNSBLs daily.
✓Check new IP addresses before using them for production sending.
✓Maintain list hygiene to avoid spam traps — the primary cause of Spamhaus listings.
✓Submit delisting requests promptly and fix the root cause first.
✓Use dedicated IPs for high-volume transactional email to isolate reputation.
✓Review bounce codes — 550 5.7.1 and 554 codes often name the blacklist in the message.
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