What causes false positives when checking domains against the Spamhaus SBL?
Summary
What email marketers say9Marketer opinions
Email marketer from SparkPost explains that if a new IP address is not properly warmed up before sending large volumes of email, ISPs may view this as suspicious activity and flag the IP, leading to a listing. This can occur even if the emails are legitimate.
Email marketer from Reddit mentions that dynamic IP addresses assigned by ISPs can sometimes be previously used by spammers. If a new user inherits such an IP, their emails might be blocked due to the IP being on the SBL, leading to a false positive.
Email marketer from MXToolbox explains that a domain's presence on a DNS blacklist is influenced by factors such as email content, sending volume, and the domain's reputation. A sudden increase in sending volume or the inclusion of spam-like keywords can trigger a listing. This can be a false positive due to a sudden campaign or promotion.
Email marketer from HostGator Forum mentions that shared servers can lead to IP reputation issues. If one user sends spam, the entire server's IP could be blacklisted, causing false positives for other users on the same server.
Email marketer from Stack Overflow explains that false positives can occur when a domain is on a shared hosting server. If one user on that server engages in spamming activity, the entire server's IP address may be listed on the SBL, affecting all domains hosted on that server.
Email marketer from SendGrid explains that new domains often have a lower reputation, making them more likely to be flagged as spam. This is due to a lack of historical data and trust. A legitimate domain might be incorrectly flagged early on because of this lack of reputation.
Email marketer from Email Geeks shares that many tools, not just providers, use SBL in a similar way. MXtoolbox is an example, and its popularity with laymen makes it suboptimal and difficult to explain.
Email marketer from Quora mentions that if a website gets hacked and is used to send spam, it can lead to a listing on the SBL. Once the site is cleaned up, getting delisted can take time, leading to continued false positives in the interim.
Email marketer from EmailAuth.io shares that a misconfigured DNS record (SPF, DKIM, DMARC) can lead to email authentication failures, causing legitimate emails to be flagged as spam. A typo in the SPF record, for instance, can cause a false positive and lead to an SBL listing.
What the experts say4Expert opinions
Expert from Spam Resource explains that one cause of false positives is short-term blacklistings. These can occur when filters temporarily misinterpret traffic patterns or activity as malicious, leading to a brief period where a domain or IP is listed before being removed when the issue resolves itself or is corrected.
Expert from Word to the Wise explains that legitimate email can be marked as spam when it lacks a clear, verifiable identity. This includes proper authentication (SPF, DKIM, DMARC) and a consistent sending reputation. Without these, even non-spam content can be filtered due to looking suspicious to automated systems.
Expert from Email Geeks explains that <http://scarlet.be|scarlet.be> is doing something unusual with the SBL, resolving the domain IP and checking it against the SBL, which is not the intended use and leads to false positives.
Expert from Email Geeks shares a link to a SBL listing on Spamhaus related to fonts.googleapis.com: <https://www.spamhaus.org/sbl/query/SBL515305>.
What the documentation says5Technical articles
Documentation from HetrixTools.com shares that domains can be blocklisted because of malware distribution, phishing activity, spam traps, or a hacked website. False positives can occur because systems misinterpret these signs, and sometimes a network issue can be falsely identified as malicious.
Documentation from Cisco Talos says spam detection mechanisms can sometimes misclassify legitimate emails as spam based on algorithms and patterns. For example, if new sending infrastructure has no reputation, this can impact deliverability even if sending legitimate emails.
Documentation from Spamhaus.org explains that the SBL (Spamhaus Block List) lists IP addresses and domains based on verifiable evidence of spamming or other malicious activities. False positives can occur if a server is temporarily compromised and used for spamming without the owner's knowledge, leading to a listing based on observed behavior.
Documentation from Proofpoint says that URL patterns in emails, especially if shortened or obfuscated, can trigger spam filters. Legitimate emails with URLs that resemble spam patterns may be incorrectly flagged.
Documentation from MultiRBL shares that IP addresses can be listed due to spam complaints, spam trap hits, or being part of a compromised network. False positives are possible if the system incorrectly attributes spam activity to an IP or if there's a delay in removing a listing after the issue is resolved.