What does it mean when Free.fr SMTP responses show an IP as blacklisted on Spamhaus PBL even though it's not?
Michael Ko
Co-founder & CEO, Suped
Published 22 Jun 2025
Updated 16 Aug 2025
5 min read
Receiving an SMTP bounce message from a mail server, like Free.fr, stating that your IP address is blacklisted on Spamhaus PBL (Policy Blocklist) can be confusing, especially when a direct lookup on the Spamhaus website shows no such listing. This discrepancy often points to an issue beyond a simple blocklist entry.
This situation is more common than you might think, and it highlights the complexities of email deliverability and how different mail servers interpret and enforce anti-spam measures. It's crucial to understand the nuances of how these systems interact to diagnose and resolve such issues effectively.
Before diving into the specifics of the Free.fr error, let's briefly review what the Spamhaus Policy Blocklist (PBL) is. The PBL is a blocklist (or blacklist) of IP addresses that should not be sending email directly to the internet. These are typically IP addresses assigned to residential broadband users or dynamic IP addresses which are not expected to be used for sending outgoing mail directly, but rather through an ISP's designated mail server.
The purpose of the PBL is to prevent spam from compromised consumer machines, which often send mail directly without proper authentication. If an IP address listed on the PBL attempts to send email directly to a recipient's mail server, it will likely be rejected. However, legitimate users on these networks can send mail if they use their ISP's authenticated SMTP server.
It's important to note that being on the PBL doesn't necessarily mean your IP is a source of spam or has a bad reputation in the traditional sense. It simply means that, by policy, email should not originate directly from that IP address. This is a key distinction from other blocklists, like the Spamhaus Exploits Blocklist (XBL), which lists IPs infected with malware or compromised devices.
Understanding PBL policy
The Policy Blocklist (PBL) aims to block unauthenticated direct-to-MX email from consumer IP ranges. If your email server is operating from one of these IP ranges, you must route your mail through an authenticated smart host provided by your ISP or mail service provider.
Diagnosing the Free.fr anomaly
The core of the problem, as described, is receiving an SMTP response from Free.fr that indicates a Spamhaus PBL listing, even when a direct lookup confirms your IP isn't listed. This suggests the issue is likely not with Spamhaus itself, but rather how Free.fr's mail servers are processing or interpreting blocklist data.
One common reason for such a discrepancy is an invalid response code or a misconfiguration on Free.fr's side. If their system is encountering an internal error while performing a DNSBL lookup, it might incorrectly default to a generic "blacklisted on Spamhaus PBL" message, even if the actual lookup result is clean or ambiguous. This behavior has been observed with other providers too.
The SMTP response you're seeing often includes phrases like invalid response code or connection failed. This specific wording suggests a problem in Free.fr's interaction with the Spamhaus DNSBL (or any other DNSBL they use), rather than a definitive listing. The error message is a symptom of their internal system failing to correctly query or interpret the blocklist data.
Example Free.fr SMTP Bounce Messagetext
499 4.0.0 unable to connect to MX servers: - mx1.free.fr: connection failed: while reading response: invalid response code: The IP xxx.xxx.xxx.xx is blacklisted on Spamhaus PBL
Scenario A: IP genuinely listed
Your IP would consistently appear on the Spamhaus PBL website when you perform a direct lookup. The bounce message would likely be clearer, without references to invalid response codes or connection failures. Remediation would involve direct delisting requests or routing through an authenticated SMTP relay.
Scenario B: Free.fr's error
Your IP does not appear on the Spamhaus PBL check, but Free.fr's SMTP response includes phrases like invalid response code. This indicates a transient or systemic issue on Free.fr's end. Your primary action should be to contact Free.fr's postmaster team.
Troubleshooting steps
When faced with such an ambiguous bounce message, the first and most critical step is to confirm the actual blocklist status of your IP. Use the official Spamhaus Blocklist Checker to see if your IP is truly listed. If it's not, you have strong evidence that the issue lies with the receiving server, in this case, Free.fr.
The next step is to contact Free.fr's postmaster team. Provide them with the full SMTP bounce message, including the invalid response code and the specific IP address in question. Explain that you have verified the IP is not listed on Spamhaus PBL. Their postmaster team should be able to investigate the internal error on their side that's causing this misleading bounce.
While awaiting their response, ensure your sending infrastructure is compliant with best practices. Even if the immediate issue is Free.fr's error, a well-configured sending setup reduces the chances of legitimate blocklist issues in the future. This includes proper SPF, DKIM, and DMARC records, and maintaining a clean sender reputation. You can also refer to our guide on how to remove your IP from Spamhaus PBL if you ever find yourself genuinely listed.
Views from the trenches
Best practices
Always verify any blocklist (or blacklist) message against the official blocklist's lookup tool.
Contact the receiving mail server's postmaster team with full bounce details and your verification.
Maintain strong email authentication (SPF, DKIM, DMARC) to build and protect sender reputation.
Common pitfalls
Assuming a bounce message is always accurate without cross-referencing with blocklist databases.
Wasting time trying to delist from Spamhaus when the problem is an internal error at the receiving end.
Ignoring the specific error codes or additional context in SMTP bounce messages.
Expert tips
Keep detailed logs of bounce messages, including full headers, for easier troubleshooting.
Understand the different types of Spamhaus lists (PBL, SBL, XBL) to correctly interpret errors.
Use email deliverability testing tools to simulate sends and identify potential issues before they impact live campaigns.
Expert view
Expert from Email Geeks says PBL is a list of consumer IP addresses that should not be originating mail directly.
2021-04-21 - Email Geeks
Marketer view
Marketer from Email Geeks says they noticed the same issue, with Free.fr SMTP responses showing an IP as blacklisted on Spamhaus PBL even though it's not, and had checked each IP without hits.
2021-04-21 - Email Geeks
Summary of the issue
When Free.fr SMTP responses incorrectly report an IP as blacklisted on Spamhaus PBL, it's typically a sign of an internal system issue at Free.fr, rather than a genuine blocklist entry against your IP. The presence of an invalid response code within the bounce message is a key indicator of this problem.
The most effective resolution is to directly engage with Free.fr's postmaster team, providing them with the exact error message. While you await their resolution, maintaining robust email sending practices will serve you well in preventing future deliverability challenges, whether they stem from genuine blocklists or transient system errors.
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