Spam Eating Monkey (SEM) blocklists are DNS-based lists (DNSBL/URIBL) used by some mail systems to flag sending IPs, domains, or URLs associated with spam-trap activity, backscatter, or very newly registered domains. If your IP or domain is listed, your email may be rejected or routed to spam by systems that consult SEM.
What is the Spam Eating Monkey (SEM) blocklist?
Spam Eating Monkey publishes multiple blocklists that identify different types of risk signals:
- IP-based DNSBLs (IPv4/IPv6): List sending IPs observed sending to spam traps or generating backscatter.
- Domain/URI-based URIBLs: List domains or URLs found in spam-trap messages.
- “Fresh” domain lists: List newly registered domains for a short period (often used as a risk heuristic).
SEM blocklists you may see referenced
- SEM-BACKSCATTER: IPs sending backscatter (typically bounces/auto-replies) with a NULL sender to spam traps. Auto-expires after ~15 days of inactivity.
- SEM-BLACK: IPs sending mail to spam traps. Auto-expires after ~15 days of inactivity.
- SEM-IPV6BL: IPv6 addresses sending mail to spam traps. Auto-expires after ~15 days of inactivity.
- SEM-FRESHZERO: Domains registered in the last 24 hours. Auto-expires after ~24 hours.
- SEM-FRESH / SEM-FRESH10 / SEM-FRESH15 / SEM-FRESH30: Newly registered domains by age threshold (about 5/10/15/30 days). Auto-expires after the same period.
- SEM-NETBLACK: Networks with low reputation. Does not expire automatically.
- SEM-URI: Domains/URIs found in spam-trap emails. Auto-expires after ~30 days of inactivity.
Why am I listed on a Spam Eating Monkey blocklist?
Common reasons include:
- Spam-trap hits: Your IP sent mail that reached SEM spam traps (often due to poor list hygiene, purchased lists, or old/unengaged lists).
- Backscatter behavior: Your server generated non-delivery reports/auto-replies to forged senders (misconfigured bounce handling can contribute).
- Newly registered domain: Your domain is legitimately new and appears on SEM-FRESH* lists temporarily.
- Low network reputation: Your IP range/network is flagged on SEM-NETBLACK, which typically indicates broader reputation issues beyond a single message.
To confirm whether you’re listed (and where), run a check with InboxAlly’s free Spam Database Lookup.
How do I get removed from SEM blocklists?
In many cases, SEM listings expire automatically once the triggering behavior stops:
- SEM-BLACK / SEM-IPV6BL / SEM-BACKSCATTER: typically drop off after ~15 days of inactivity.
- SEM-URI: typically drops off after ~30 days of inactivity.
- SEM-FRESH* lists: drop off after the defined “fresh” window (24 hours to 30 days).
- SEM-NETBLACK: may not expire automatically; remediation usually requires sustained reputation improvement.
Action steps that help removal happen faster (and prevent re-listing):
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Stop sending to bad addresses
- Remove hard bounces and unknown users immediately.
- Avoid sending to old/unengaged segments until you’ve cleaned the list.
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Fix backscatter (if applicable)
- Ensure your mail server rejects invalid recipients during the SMTP transaction (instead of accepting then bouncing later).
- Review auto-reply/bounce configurations so you’re not generating responses to forged senders.
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Reduce risky content and links
- If you’re listed on SEM-URI, audit the domains/URLs in your messages (including redirects and tracking links).
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Monitor after changes
- Re-check periodically using Spam Database Lookup.
- For ongoing monitoring, use Domain Reports in the InboxAlly app to track domain reputation and authentication status over time.
How does an SEM listing affect deliverability?
Impact depends on whether the receiving system uses SEM and how it’s configured:
- Hard blocks (rejections): Some servers may reject mail outright when an IP/domain is listed.
- Spam folder placement: Others may accept the message but route it to spam.
- Reputation spillover: Repeated listings can contribute to broader sender reputation issues, especially if the underlying cause (spam traps, backscatter, poor list hygiene) isn’t fixed.
If you’re troubleshooting a sudden drop in inbox placement, confirm listings with Spam Database Lookup and then track improvements over time in Domain Reports (InboxAlly app).
Next steps: blocklist remediation workflow
For a step-by-step process (diagnosis, fixes, and prevention), follow Blocklist Impact and Remediation.