← All articles
Email Security 2026-02-25 · 5 min read

Email Blacklists (DNSBLs): Why Your Mail Lands in Spam

DNS-based blocklists (DNSBLs) are lists of IP addresses known for sending spam. Receiving mail servers check them in real time; a listed sending IP means your messages are deprioritised, filed as spam, or refused.

How an IP gets listed

  • Sending unsolicited bulk mail or being part of a compromised network.
  • A misconfigured server acting as an open relay.
  • Sharing a hosting IP range with bad neighbours.

Staying off and getting off

Authenticate your mail (SPF, DKIM, DMARC), keep volumes consistent, secure any forms that send email, and set valid reverse DNS. If listed, fix the root cause first, then use the delisting form on the specific blocklist. The MX analyser checks your mail IPs against multiple DNSBLs and shows reverse-DNS status.

Put this into practice
Run a free, private scan — no login, nothing stored.
🛡 Web Scan 🔒 SSL/TLS 📬 MX & Email 🎣 URL Check

Related articles

Email Security SPF Records Explained: Stop Others Spoofing Your Email SPF tells the world which servers may send mail for your domain. Here is how to write one that actually protects you. Email Security DMARC: The Policy That Ties SPF and DKIM Together DMARC tells receivers what to do with mail that fails authentication — and reports who is sending as you. Here is how to roll it out. Email Security DKIM: How a Cryptographic Signature Proves Your Email Is Real DKIM adds a tamper-proof signature to your mail. Here is what it is and how to set it up correctly.