DNSprobe Wiki · IP reputation
IP reputation and blacklists (DNSBL)
This page explains how DNSprobe checks the reputation of your server’s IP address using DNS-based blacklists (DNSBL) and how to interpret the results.
Many mail providers and antispam systems consult DNS-based blacklists (DNSBL) to decide whether to accept, reject or filter email coming from a given IP address.
If the IP of your web or mail server is listed, your messages can be delayed, placed in spam, or rejected entirely.
The Reputation section of DNSprobe queries several well-known DNSBLs and summarises the status for the tested IP address.
1. Overview: what is IP reputation?
IP reputation represents the level of trust that other systems (mail providers, antispam services, hosting platforms) have in the behaviour of a given IP address.
An IP that frequently sends spam, malware, or forged messages will quickly be added to one or more blacklists and will see its emails blocked or heavily filtered.
Why monitor your IP reputation?
Monitoring your IP ensures that you detect blacklisting issues early, before your users or clients start experiencing email deliverability problems.
Where is IP reputation used?
IP reputation is used mainly by mail exchangers (MX), spam filters, and some web security services to decide whether to trust traffic coming from a given address.
2. How DNSprobe tests your IP reputation
When you run a DNSprobe analysis, the Reputation section takes the main IP address of the server and queries several DNSBL zones using DNS lookups.
Each blacklist answers either “listed” or “not listed”, sometimes with detailed codes that DNSprobe translates into a more readable description.
- Reverse the IP address (for example 173.209.56.130 becomes 130.56.209.173) and append the DNSBL zone.
- Perform a DNS A lookup on the constructed hostname via a chosen resolver.
- If the query returns one or more IPs, the original IP is considered listed on this DNSBL; otherwise, it is not listed.
- DNSprobe aggregates the answers, counts how many lists report the IP, and displays a Pass/Fail status with a textual summary.
For performance reasons, this check is done asynchronously via AJAX: you may briefly see a loader before the final Reputation result is displayed.
3. DNSBLs checked by DNSprobe
DNSprobe currently queries the following DNSBLs for each tested IP. This list may evolve over time.
| List name | DNSBL zone | Focus | Notes |
|---|---|---|---|
| Spamhaus | zen.spamhaus.org |
One of the most widely used and reputable anti-spam blacklists. | If Spamhaus lists your IP, many providers will reject or heavily filter your messages. DNSprobe also detects query-block codes (rate limits). |
| Barracuda | b.barracudacentral.org |
Barracuda Networks email security blacklist. | Delisting usually requires creating an account and submitting a removal request on Barracuda’s website. |
| SORBS | dnsbl.sorbs.net |
Historical multi-purpose blacklist with various zones (spam, open relays, dynamic IPs, etc.). | Listed entries can have a real impact, but some lists are more aggressive or controversial than others. |
| SpamCop | bl.spamcop.net |
Blacklist based largely on user spam reports and feedback from spamtraps. | Listed entries can have a real impact, but some lists are more aggressive or controversial than others. |
| PSBL | psbl.surriel.com |
Passive Spam Block List (PSBL), lightweight and relatively easy to delist from. | Listed entries can have a real impact, but some lists are more aggressive or controversial than others. |
| HostKarma | hostkarma.junkemailfilter.com |
Multi-colour list returning GOOD, NEUTRAL or BAD codes for the same IP. | DNSprobe interprets HostKarma’s return codes to show whether your IP is considered good, bad or neutral. |
| Mailspike BL | bl.mailspike.net |
Mailspike blacklist (bad reputation). | Mailspike provides both bad reputation zones (BL) and grey/spam zones (Z). |
| Mailspike Z | z.mailspike.net |
Mailspike Z (spam zone) list. | Mailspike provides both bad reputation zones (BL) and grey/spam zones (Z). |
| UCEProtect L1 | dnsbl-1.uceprotect.net |
Blacklist focused on abuse coming from IP ranges and networks. | UCEProtect is considered controversial by many administrators; some levels may list entire providers rather than individual abusive hosts. |
| UCEProtect L2 | dnsbl-2.uceprotect.net |
Blacklist focused on abuse coming from IP ranges and networks. | UCEProtect is considered controversial by many administrators; some levels may list entire providers rather than individual abusive hosts. |
| UCEProtect L3 | dnsbl-3.uceprotect.net |
Blacklist focused on abuse coming from IP ranges and networks. | UCEProtect is considered controversial by many administrators; some levels may list entire providers rather than individual abusive hosts. |
DNSprobe shows a green check mark when the IP is not listed and a red cross when the IP is listed on the corresponding blacklist.
HostKarma return codes
HostKarma uses several codes: 127.0.0.1 = GOOD (trusted IP), 127.0.0.2 = BAD (spam source), 127.0.0.3 = NEUTRAL. DNSprobe converts these into human-readable labels.
4. Score summary and interpretation
At the bottom of the Reputation section, DNSprobe summarises whether the tested IP is listed and on how many DNSBLs.
- ✅ No blacklist reports this IP: deliverability should be normal (subject to your SPF, DKIM and DMARC configuration).
- ❌ One or more DNSBLs list this IP: some providers may reject or filter your messages.
- ⚠️ Some lists are controversial (for example UCEProtect); being listed there may have less impact than on Spamhaus, but it is still a warning sign.
Always correlate blacklist information with real-world symptoms (bounced messages, spam folder, user complaints) before taking drastic actions.
5. Best practices to keep a good reputation
Keeping a clean IP reputation is an ongoing process rather than a one-time task. Here are a few practical recommendations:
- Secure your mail server (no open relays, authentication required, rate limiting, strong passwords, etc.).
- Monitor outgoing traffic and logs to quickly detect compromised accounts or sites sending spam.
- Use proper SPF, DKIM and DMARC records to prove that your emails are legitimate.
- Avoid purchasing mailing lists or sending unsolicited bulk email from your production servers.
- If your IP is listed, follow the delisting procedure provided by each blacklist and fix the underlying cause before trying again.
If your hosting provider offers a dedicated IP or can move your account to a different IP, this may help in severe cases – but only if the original problem has been fully resolved.
6. Limitations and special cases
Not all DNSBLs are equal. Some are very reputable and widely used, others are experimental, abandoned or considered abusive.
DNSprobe deliberately includes some controversial services (such as UCEProtect) in order to give a complete picture, but their presence does not automatically mean that your IP is unusable.
- A listing can be temporary (for example after a short-lived spam burst) and automatically removed after a few days.
- Some DNSBLs list entire ranges or providers, which you cannot fix yourself; only the upstream provider can act.
- Conversely, being completely clean does not guarantee perfect deliverability if your domain reputation or email content is problematic.
Use the Reputation report as an indicator and a diagnostic aid, not as the sole decision-maker.
In short
DNSprobe’s Reputation section quickly tells you whether the tested IP appears on major DNS-based blacklists and on how many of them.
If issues are detected, combine this information with your SMTP logs, SPF/DKIM/DMARC configuration and feedback from your users to plan the right corrective actions.
Need help interpreting these results?
If you see that your IP is listed or if you are experiencing recurring deliverability issues, contact your hosting provider or email administrator. DNSprobe highlights the problems, but only configuration changes, abuse cleanup and long-term monitoring will permanently fix reputation issues.