What this check looks at
JoltMx queries the connecting IP against a configured set of DNS blocklists (by default Spamhaus ZEN and SpamCop). For each zone it reports whether the IP is listed, clean, or whether the lookup couldn't be completed.
The check fails open: a zone that can't be queried - or that answers with an error code (often because a public/rate-limited resolver is in use) - is reported as Info, never as a false "listed." Your IP is never marked dirty just because a lookup was inconclusive.
Why it matters
A blocklist listing is one of the bluntest deliverability problems there is - most receivers reject or junk listed IPs before they even look at authentication. Listings happen for many reasons: a compromised server on the same IP, a spam run from a shared host, or a dirty IP inherited from a previous tenant.
How the diagnostic grades it
| Result | Severity | What it means |
|---|---|---|
| Not listed | Pass | The IP is clean on the zones that answered. |
| Listed on a blocklist | Critical | The IP is listed - rejected or junked by most receivers. Request delisting. |
| Could not check a zone | Info | A lookup returned an error code (often a public resolver). Not confirmed either way. |
| Private / uncaptured IP | Info | A local or missing address - blocklists don't apply. |
How to fix it
- Visit the blocklist operator's site (it's named in the finding) to see the listing reason.
- Fix the underlying cause - secure the server, stop the spam source, close an open relay - then request delisting.
- If you've inherited a dirty IP from a host, ask for a clean one or warm up a new sending IP.
Related checks
Reverse DNS · Policy disposition · Deliverability vs placement