Blacklist & Reputation Monitoring
Know immediately if your IP or domain is blacklisted.
Blacklist listings silently destroy email deliverability. A single compromised account, a spam complaint spike, or an inherited reputation problem can land your sending IPs on major blocklists before you know it's happening. NetTests checks your IPs and domains against 50+ blocklists on a schedule and alerts you the moment a new listing appears.
Blacklist listings are invisible until the damage is done
When a sending IP is listed on a major blocklist, messages destined for ISPs that subscribe to that list begin failing silently. Recipients may never see a bounce — messages simply disappear. Without active monitoring, the first sign of a blacklist listing is often a sharp drop in open rates or a client reporting that they aren't receiving emails, by which point significant damage to sender reputation may have occurred.
Listings happen for reasons that often have nothing to do with your own sending practices. A single compromised account on your mail server can generate enough spam to trigger a listing within hours. On shared hosting or a shared sending IP, another tenant's bad behavior can get your traffic blocked too — you inherit a reputation problem you never caused. Even a legitimate marketing send can cross a complaint-rate threshold on a strict blocklist if a mailing list hasn't been cleaned in a while.
Blacklist monitoring provides the earliest possible warning. By checking against all major blocklists on a schedule, NetTests detects new listings within hours — giving you time to investigate the cause, remediate the issue, and begin the delisting process before the impact on deliverability becomes severe.
What NetTests blacklist monitoring checks
NetTests checks your sending IP addresses and domains independently against more than 50 widely-used DNS-based blocklists (DNSBLs) — including Spamhaus, SORBS, Barracuda, and SpamCop — on a schedule you control. IPs and domains are tracked separately because they're listed independently: a domain can be clean while its sending IP is blocked, or the reverse, and each requires its own remediation path.
Every check records which lists, if any, currently list each target, so a new listing shows up as a change from the last check rather than something you have to notice on your own. The dashboard keeps a full history of listings and delistings, which is useful for spotting a recurring pattern — an IP that gets listed every few weeks usually points to an ongoing hygiene problem worth investigating, not a one-off incident.
Alerts reach your team through email, Slack, Microsoft Teams, or SMS the moment a new listing is detected, with enough detail to start the delisting process immediately instead of losing hours diagnosing a sudden drop in delivered mail.
Key features
50+ blocklist checks
Check against Spamhaus, SORBS, Barracuda, SpamCop, and dozens of other widely-used blocklists.
IP and domain monitoring
Monitor sending IP addresses and domain names independently — both can be listed on different blocklists.
Immediate new-listing alerts
Receive notifications as soon as a new listing is detected — before deliverability impact accumulates.
Listing history
Track when your IPs and domains have been listed and delisted over time — useful for diagnosing recurring reputation problems.
Multi-IP coverage
Track every sending IP across every mail server you operate, not just one address.
Change detection
A new listing is flagged as a change since the last check, not buried in a long status report.
Multi-channel alerts
Reach your team through email, Slack, Microsoft Teams, or SMS the moment a listing appears.
Full check history
Every run logged with timestamps — confirm exactly when a listing started and when delisting actually took effect.
What you'll see
A live look at blocklist status across your sending IPs, and the alert that fires when a new listing appears.
Not ready to commit?
Try the free IP Blacklist Check first. Check a single IP against 49 major DNS blacklists, then set up continuous monitoring across every sending IP you operate.
Try the free tool →Free reputation tools
Check an IPv4 address against 49 major DNS blacklists (Spamhaus, SORBS, Barracuda, SpamCop, etc.).
Resolve a domain's MX hosts to IPs and check each against 49 IP blacklists plus 9 domain blacklists.
Comprehensive email domain scorecard including blacklist status and authentication records.
Frequently asked questions
What is a DNS blacklist (DNSBL)?
A DNS blacklist is a published list of IP addresses or domains flagged as sources of spam or abuse, queryable via a special DNS lookup. Mail servers check incoming connections against one or more DNSBLs before accepting a message — a listed IP is often silently rejected or routed to spam without ever generating a bounce the sender can see.
Why did my IP get listed if I didn't send spam?
Common causes that have nothing to do with your own sending: a compromised account on your mail server generating spam without your knowledge, sharing an IP with another sender on the same host or ESP whose traffic triggered the listing, or crossing a strict blocklist's complaint-rate threshold from an otherwise-legitimate send to a stale list.
How long does delisting take?
It varies by blocklist. Some, like Spamhaus, offer a self-service removal request that clears in hours once the underlying issue is fixed. Others use automatic time-based expiry and delist on their own after a period of clean sending, typically anywhere from a few hours to several days. Continuous monitoring tells you the moment delisting actually takes effect, rather than guessing when it's safe to resume sending.
Does a listing affect all my email at once?
No — only mail routed through the listed IP or domain, and only to recipients whose mail provider actually subscribes to that specific blocklist. A listing on one blocklist might cause failures at some ISPs while others deliver normally, which is part of why listings are so easy to miss without dedicated monitoring: the damage looks partial and inconsistent rather than a clean outage.
Should I monitor a shared or dedicated sending IP differently?
Shared IPs are worth monitoring more closely, since a listing can come from someone else's traffic entirely — your own sending hygiene doesn't fully protect you. Dedicated IPs put reputation entirely in your own hands, which is safer long-term but means any mistake is fully yours to fix. Either way, the monitoring itself works the same: check on a schedule, alert on any new listing.
Monitor your reputation before customers notice
NetTests checks your IPs and domains against 50+ blocklists on a schedule and alerts you immediately on any new listing.
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