| # | Target | DNSBL | Status | Return | Evidence | TTL | Time (ms) | Copy |
|---|---|---|---|---|---|---|---|---|
| {{ index + 1 }} | {{ row.ip }} | {{ row.listName }} | {{ statusLabel(row.status) }} | {{ row.response || '—' }} | {{ row.evidence }} — | {{ row.ttl === null || typeof row.ttl === 'undefined' ? '—' : row.ttl }} | {{ row.ms === null || typeof row.ms === 'undefined' ? '—' : row.ms }} |
Email blocklists are shared lists of sending hosts and addresses that help mail systems filter unwanted traffic, and checking your own infrastructure can explain delivery issues and guide remediation. Results indicate whether a host or address appears on selected lists and show short reason text when available, so you can decide what to fix first.
You provide a mail host or an address and choose the lists to query, then the checker resolves the target and tests each list, returning a simple table and two charts that summarize outcomes and response times. A quick scan supports day to day monitoring and incident review without extra tooling or long setup.
A practical example is an operations review after bounce spikes from a new outbound server where a short run confirms a single listing and retrieves the reason text, so you can file a removal request and verify the change later. Be aware that each list has its own policy and cadence, so a clear status today can change tomorrow and evidence text may vary by provider.
For consistent comparisons, test at similar times of day, keep inputs stable, include both address families if your mail servers publish newer records, and repeat checks after any configuration change.
The checker measures presence on common mail blocklists for one or more IP addresses resolved from a host. Outcomes are grouped into listed, clear, error, or skipped, and each lookup records elapsed time in milliseconds to help spot slow or failing resolvers.
Computation follows the standard query pattern used by DNS based lists. For IPv4 the octets are reversed before querying a list zone. For IPv6 the address is expanded to eight hextets, converted to nibbles, then reversed and queried. An A record indicates a listing. When enabled, TXT records are fetched to capture human readable evidence.
Interpretation is direct. Any returned address marks a listing. An explicit negative response is treated as clear. Transport or resolver failures surface as error. Lists that do not support the target address family are skipped. Summaries aggregate counts across all addresses and lists selected.
Comparability depends on selections and address family support. Some lists support both families while others only IPv4, so the IPv6 resolution option changes totals. Hostnames are resolved first to addresses, then each address is checked against each chosen zone.
| Symbol | Meaning | Unit/Datatype | Source |
|---|---|---|---|
t_ms |
Elapsed time per lookup | ms, integer | Derived from performance timer |
TTL |
Time to live from first answer | integer | Returned by resolver |
code |
Resolver status code | integer | Returned by resolver |
| Status | Interpretation | Action Cue |
|---|---|---|
| Listed | Target appears on the provider list; TXT may describe why. | Review evidence, remediate, then request removal. |
| Clear | No listing returned by the provider at query time. | Recheck after changes or if complaints persist. |
| Error | Resolver or transport failure prevented a decision. | Retry later or switch resolver; inspect timeouts. |
| Skipped | List does not support the target address family. | Use IPv4, or enable IPv6 resolution when available. |
| Name | Zone | IPv4 | IPv6 |
|---|---|---|---|
| Spamhaus ZEN | zen.spamhaus.org | yes | yes |
| SpamCop | bl.spamcop.net | yes | no |
| SORBS | dnsbl.sorbs.net | yes | no |
| UCEPROTECT Level 1 | dnsbl-1.uceprotect.net | yes | no |
| PSBL | psbl.surriel.com | yes | no |
| SPAMRATS | all.spamrats.com | yes | no |
| DroneBL | dnsbl.dronebl.org | yes | no |
| SPFBL | dnsbl.spfbl.net | yes | yes |
| HostKarma | hostkarma.junkemailfilter.com | yes | no |
| Invaluement ivmSIP | ivmSIP.invaluement.com | yes | no |
You can select all, clear, or restore defaults. Lists that lack IPv6 support are automatically skipped when only IPv6 addresses are available.
| Field | Type | Min | Max | Step/Pattern | Error Text | Placeholder |
|---|---|---|---|---|---|---|
| Host or IP | string | — | — | IPv4: ^(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})$ with octets 0–255; IPv6: compressed or eight hextets. |
Enter a hostname or IP address to check. / No usable IP addresses found for the provided input. | mail.example.com or 203.0.113.45 |
| DNSBL catalog | multi select | 0 | 10 | Defaults preselect seven lists. | Select at least one DNSBL before running the check. | List names shown above |
| Fetch TXT evidence | boolean | — | — | Off queries only A; On also queries TXT on listings. | — | — |
| Resolve IPv6 (AAAA) | boolean | — | — | Adds AAAA resolution for hostnames. | — | — |
Units and rounding: elapsed time is measured in whole milliseconds; TTL and resolver status codes are reported as returned; the decimal separator is a dot where present.
| Input | Accepted Families | Output | Encoding/Precision | Rounding |
|---|---|---|---|---|
| Hostname or IP | Hostname, IPv4, IPv6 | Table, charts, JSON, CSV, DOCX | JSON pretty print; CSV RFC style rows | Time rounded to integer ms |
Networking and storage: lookups are performed from the browser against public DNS over HTTPS endpoints with fallback between Cloudflare and Google. A and AAAA resolution uses a 5 000 ms timeout and list A or TXT queries use 6 000 ms. No application server stores your inputs.
Performance and complexity: for N addresses and M lists the check count is N × M. Charts render from aggregated results. Controls include copy and download for CSV or JSON and a DOCX report export.
Diagnostics and determinism: identical inputs typically yield identical outputs at a given moment, though list content and resolver behavior can change between runs. The summary includes a local timestamp for context.
Security considerations: evidence strings are treated as text. No credentials are used. Avoid pasting sensitive internal hostnames into third party resolvers unless permitted by policy.
Requests are issued from your browser to public resolvers; the app does not persist inputs to a server. Use in line with organizational acceptable use and email policies.
Blocklist status checks for mail hosts and addresses with shareable evidence.
Example: mail.example.com with defaults runs seven lists and reports any evidence text found.
No application server stores inputs. Lookups are issued from your browser to public resolvers configured in the code.
Accuracy depends on each provider policy. Treat evidence as guidance and verify operational causes like open relays or misconfiguration.
The selected list does not support the target address family, so it is not queried for that target.
Lookup time is in whole milliseconds. TTL and status codes are shown as reported by the resolver.
No. Network access to the configured public resolvers is required.
There is no pricing logic in the package. Usage of third party lists may be subject to their terms.
Enable the IPv6 resolution option in Advanced to add AAAA lookups for hostnames and include IPv6 capable lists in the run.
Near zero listings across many checks usually indicate healthy sending. One list with a reason text suggests a targeted remediation and follow up run.