DNS Blacklist Monitoring

A DNSBL monitor checks whether a target IP is listed on one or more public spam blacklists, using the same reversed-octet DNS query every mail server already relies on for this (e.g. 4.3.2.1.zen.spamhaus.org for IP 1.2.3.4). If your outbound mail server's IP gets listed, other mail servers may start silently rejecting or spam-foldering everything you send — this catches that before it becomes a support ticket avalanche.

Availability

Available on every plan — a handful of DNS queries per check costs nothing like Synthetic Monitoring's browser.

How it works

The target can be an IP address directly, or a hostname (resolved to its first IPv4 address — the same "check the thing that actually sends mail" shape as pointing a check at your mail server's hostname).

curl -X POST https://api.monsphere.com/api/v1/organizations/{orgId}/monitors \
  -H "X-Api-Key: msk_live_..." -H "Content-Type: application/json" \
  -d '{
    "name": "Mail Server Reputation",
    "type": "dnsbl",
    "target": "mail.example.com",
    "intervalSeconds": 3600,
    "timeoutSeconds": 30,
    "config": {
      "dnsblZones": ["zen.spamhaus.org", "bl.spamcop.net"],
      "dnsblFailThreshold": 1
    }
  }'

• dnsblZones — which blacklists to check. Leave it out to use a small default set of well-known public zones.
• dnsblFailThreshold — how many of the checked zones must list the target before the check fails (default 1 — being on any single blacklist is worth knowing about, but you can raise this to reduce noise from one low-reputation-only list).

A blacklist zone's own DNS server timing out or erroring doesn't count as either "listed" or "clean" for that zone — it's excluded from the result and reported separately, so a flaky public blacklist can never produce a false "you're clean" result.

IPv4 only

IPv6 DNSBL uses a much longer nibble-reversed query format that many zones don't even support — this check is IPv4 only for now.

How it runs

Like Synthetic, WHOIS, and API Transaction monitors, a DNSBL monitor doesn't go through Blackbox Exporter or Prometheus — checking several blacklist zones and aggregating the results isn't something a single Blackbox DNS probe can express. It runs on MonSPHERE's own internal scheduler, so there's no region to pick.