Blacklist
A database of IP addresses or domains identified as spam sources, used by email providers to block mail.
Definition
A blacklist (also called blocklist or denylist) is a real-time database of IP addresses, domains, or email addresses identified as spam sources. Email providers and spam filters query these lists to decide whether to accept, filter, or reject incoming mail. Being blacklisted can devastate your email deliverability, causing your messages to be blocked across many recipients.
Why It Matters
Landing on a blacklist can cause immediate and severe deliverability problems. Your emails may be rejected outright or consistently filtered to spam. Major blacklists like Spamhaus are trusted by thousands of mail servers. Even a brief listing can take days to resolve and permanently affect sender reputation.
How It Works
Blacklists are maintained by anti-spam organizations that track spam complaints, spam trap hits, and malicious behavior. When your IP or domain is added, mail servers that query that list may block or filter your emails. Each blacklist has its own listing criteria, severity, and removal process.
Best Practices
- 1Monitor major blacklists regularly using tools like MXToolbox
- 2Never purchase or scrape email lists
- 3Remove invalid addresses and complainers promptly
- 4Investigate and resolve the root cause before requesting removal
- 5Use a dedicated IP for marketing if you send high volume