Summary
False positives when checking domains against the Spamhaus SBL arise from a confluence of factors. These include unconventional uses of the SBL for checking domains, shared hosting environments where the actions of one user can impact others, the inheritance of dynamic IPs previously used for spam, sudden increases in email volume, the use of spam-like keywords, misconfigured DNS records, compromised websites sending unauthorized emails, inadequate IP warming procedures, temporary misinterpretations of traffic patterns by filters, and a lack of clear email identity (authentication and sending reputation). These situations often lead to legitimate emails being incorrectly flagged as spam.
Key findings
- Unconventional SBL Use: Some services use the SBL in non-standard ways, increasing the likelihood of false positives.
- Shared Hosting Risks: In shared hosting, if one user engages in spam activity, the entire server's IP may be blacklisted, affecting all domains.
- Dynamic IP Issues: New users inheriting dynamic IPs previously used by spammers may experience deliverability problems.
- Volume & Content Triggers: Sudden increases in email volume and the use of spam-like keywords can trigger false positives.
- DNS Misconfiguration: Incorrectly configured DNS records (SPF, DKIM, DMARC) can lead to authentication failures and false positives.
- Compromised Sites: Hacked websites used for sending spam can lead to SBL listings, impacting legitimate email.
- IP Warming Neglect: Failure to properly warm up a new IP address can cause it to be flagged as suspicious.
- Short-Term Listings: Filters can temporarily misinterpret traffic, leading to short-term blacklistings and false positives.
- Email Identity: Legitimate emails lacking proper authentication and a consistent sending reputation are more likely to be flagged as spam.
Key considerations
- Monitor SBL Usage: Understand how the SBL is being used and potential for non-standard implementations to cause errors.
- Dedicated IP: Consider using a dedicated IP address instead of shared hosting to avoid issues with other users' activities.
- IP Reputation: Monitor your IP reputation and ensure it remains positive.
- Volume Management: Avoid sudden spikes in email sending volume and carefully select keywords to prevent triggering spam filters.
- Implement Authentication: Ensure that SPF, DKIM, and DMARC records are correctly configured to authenticate your emails.
- Site Security: Keep your website secure to prevent unauthorized spam sending.
- IP Warming Strategy: Develop and implement a proper IP warming strategy when using new IP addresses.
- Monitor Listings: Check if your domain or IP is listed on any blacklists and take steps to get delisted if necessary.
- Consistent Sending: Establish and maintain a consistent sending reputation by sending high-quality, relevant content to engaged subscribers.
What email marketers say
9 marketer opinions
False positives when checking domains against the Spamhaus SBL can arise from various factors, including shared hosting environments where one user's spam activity affects others, the inheritance of dynamic IPs previously used by spammers, sudden increases in email sending volume or the use of spam-like keywords, IP reputation issues on shared servers, low reputation of new domains, misconfigured DNS records, compromised websites used for spam, and inadequate IP warming practices for new IP addresses. These scenarios often lead to legitimate emails being incorrectly flagged as spam due to circumstances beyond the sender's direct control.
Key opinions
- Shared Hosting Risks: Shared hosting environments can lead to false positives if other users on the same server engage in spamming activities.
- Dynamic IP Inheritance: Dynamic IPs previously used by spammers can cause a new user's emails to be blocked.
- Sudden Volume Spikes: Sudden increases in email volume or the use of spam-like keywords can trigger false SBL listings.
- New Domain Reputation: New domains often lack sufficient reputation, leading to higher chances of being flagged as spam.
- DNS Configuration: Misconfigured DNS records can cause authentication failures and false positives.
- Compromised Websites: Hacked websites used for spamming can lead to SBL listings and subsequent false positives.
- IP Warming Importance: Inadequate IP warming for new IPs can result in ISPs flagging the IP as suspicious.
Key considerations
- Monitor Sending Reputation: Regularly monitor your domain and IP reputation to identify potential issues early.
- Proper DNS Configuration: Ensure correct SPF, DKIM, and DMARC records are in place to authenticate your emails.
- Gradual IP Warming: Implement a gradual IP warming strategy when using new IP addresses for sending emails.
- Secure Websites: Maintain website security to prevent hacking and unauthorized spam sending.
- Consider Dedicated IPs: For high-volume senders, using dedicated IPs can mitigate the risks associated with shared hosting.
- Monitor Blacklists: Monitor blacklists to identify and resolve issues promptly.
- Email Content Review: Review email content to avoid spam-like keywords and patterns that may trigger filters.
Marketer view
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.
25 Oct 2022 - SparkPost
Marketer view
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.
21 Aug 2023 - Reddit
What the experts say
4 expert opinions
False positives when checking domains against the Spamhaus SBL can stem from various sources. Scarlet.be's unusual method of checking domains by resolving their IPs and comparing them to the SBL can lead to incorrect listings. Short-term blacklistings, where filters temporarily misinterpret traffic, also contribute to the issue. Finally, legitimate emails lacking clear identity markers such as proper authentication (SPF, DKIM, DMARC) and a consistent sending reputation may be incorrectly flagged as spam.
Key opinions
- Unconventional SBL Use: Non-standard methods of checking domains against the SBL, like that of Scarlet.be, can cause inaccurate listings.
- Temporary Misinterpretations: Short-term blacklistings due to filters temporarily misinterpreting traffic patterns can result in false positives.
- Identity and Authentication: Legitimate emails lacking proper authentication and a consistent sending reputation are more likely to be marked as spam.
Key considerations
- Monitor SBL Usage: Be aware of services or systems that might be using the SBL in non-standard ways, and understand the potential for false positives.
- Understand Short-Term Listings: Recognize that temporary blacklistings can occur and may resolve themselves quickly; avoid immediate overreaction.
- Implement Email Authentication: Ensure proper email authentication (SPF, DKIM, DMARC) and maintain a consistent sending reputation to avoid being flagged as spam.
Expert view
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.
6 Mar 2022 - Spam Resource
Expert view
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.
30 May 2023 - Word to the Wise
What the documentation says
5 technical articles
False positives when checking domains against the Spamhaus SBL can arise from various factors. Legitimate servers can be temporarily compromised and used for spamming without the owner's knowledge, leading to listings based on observed behavior. Systems can misinterpret signs of malware distribution, phishing activity, or spam traps, and even network issues can be falsely identified as malicious. Spam detection mechanisms may misclassify legitimate emails based on algorithms and patterns, especially if the sending infrastructure is new and lacks reputation. IP addresses can be listed due to spam complaints, spam trap hits, or being part of a compromised network, with false positives occurring if spam activity is incorrectly attributed or if there's a delay in removing a listing. Finally, URL patterns in emails, particularly shortened or obfuscated URLs, can trigger spam filters and incorrectly flag legitimate emails.
Key findings
- Compromised Servers: Legitimate servers temporarily compromised and used for spamming can lead to false positives.
- Misinterpretation of Signs: Systems can misinterpret signs of malware, phishing, or network issues, leading to incorrect listings.
- Algorithmic Misclassification: Spam detection algorithms can misclassify legitimate emails, especially from new sending infrastructures.
- Incorrect Attribution: IP addresses can be falsely listed due to incorrect attribution of spam activity.
- URL Pattern Triggers: Certain URL patterns, especially shortened or obfuscated ones, can trigger spam filters and cause false positives.
Key considerations
- Monitor Server Security: Regularly monitor and secure servers to prevent compromise and unauthorized spam sending.
- Review Detection Systems: Understand how spam detection systems interpret signals and adjust configurations to reduce misinterpretations.
- Establish Sending Reputation: Establish a good sending reputation, especially when using new sending infrastructures, to avoid being flagged as spam.
- Ensure Accurate Attribution: Implement measures to ensure accurate attribution of spam activity to prevent incorrect listings.
- Use Clear URLs: Avoid using overly shortened or obfuscated URLs in emails to reduce the likelihood of triggering spam filters.
Technical article
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.
22 Mar 2024 - HetrixTools.com
Technical article
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.
5 Dec 2022 - Talos Intelligence
Besides Spamhaus, what blocklists are important for email marketers to monitor?
How can I get delisted from Spamhaus?
How can I get help with a Spamhaus listing delisting?
How can I report fraudulent emails and domains to Spamhaus and other relevant organizations?
How do I check Spamhaus for my IP address and understand the listings?
How does Spamhaus decide whether to list a subdomain or a whole domain on the DBL?
