Email (or "spam") blacklists are lists mail providers consult to decide whether to accept, quarantine, or reject incoming mail from a given domain or IP.
How to check
- Use a multi-list blacklist checker — there are dozens of independent blacklists (Spamhaus, Barracuda, SORBS, etc.), and being clean on one says nothing about the others
- Check your mail provider’s own deliverability dashboard if it offers one
Common causes of landing on one
- A compromised account sending spam without the owner’s knowledge
- Missing or misconfigured SPF/DKIM/DMARC
- A sudden, unexplained spike in send volume, which pattern-matches spam behavior even if legitimate
FAQ
Does one blacklist listing affect all my email delivery?
No — each mail provider decides which blacklists to consult, so a listing might affect delivery to some recipients (e.g. one corporate mail server) but not others.