How do I identify what spam filter a company is using?

Summary

Identifying a company's spam filter involves a multifaceted approach, combining technical analysis, testing, and understanding of major email security providers. Analyzing rejection messages, SMTP logs, and MX records helps reveal filtering mechanisms. Tools like MXToolbox, GlockApps, Litmus, Snov.io, Mailjet, SendPulse, and Gmass aid in testing deliverability, checking blacklists, monitoring IP reputation, and setting up seed lists. Analyzing SPF, DKIM, and DMARC records offers insights into authentication practices. Resources like Spamhaus blocklists provide valuable data. Documentation from Microsoft (EOP), Google Workspace, Cisco (ESA), Barracuda, and Proofpoint explain their respective filtering techniques. When facing blocks, examining error messages and URLs from blocklist operators is crucial. Seed lists offer insights but require diverse seeds from multiple providers. Lastly, recognizing the complexity of Outlook's delivery is vital.

Key findings

  • Rejection Analysis: Analyzing rejection messages and SMTP logs helps uncover spam filtering details.
  • Infrastructure Checks: Checking MX records and IP ownership identifies mail servers and potential filtering services.
  • MXToolbox: MXToolbox helps identify mail servers and filtering services through domain name analysis.
  • Authentication Records: Analyzing SPF, DKIM, and DMARC records reveals authentication practices and potential spam filters.
  • Spamhaus Blocklists: Spamhaus maintains blocklists to identify spam sources.
  • Deliverability Testing: GlockApps and Litmus test email deliverability and identify spam filter triggers.
  • Blacklist Checks: Snov.io offers tools for blacklist checks to identify potential spam filtering issues.
  • IP Reputation: Mailjet monitors IP reputation, revealing potential spam filter triggers.
  • Seed Lists: Gmass suggests seed list testing to identify providers filtering emails as spam.
  • Email Testing Tools: SendPulse offers email testing tools to check deliverability and identify spam triggers.
  • Major Provider Techniques: Microsoft EOP, Google Workspace, Cisco ESA, Barracuda, and Proofpoint documentation reveals their filtering techniques.
  • Blocklist Information: Examining error messages and URLs from blocklist operators provides details when blocked.

Key considerations

  • Combine Methods: Employ a combination of methods for a comprehensive understanding of spam filtering practices.
  • Error Message Specificity: Error messages vary in detail, necessitating careful analysis.
  • Statistical Significance: Interpret seed list results cautiously due to limited statistical significance.
  • Provider Relationships: Seed provider relationships with mailbox providers influence seed weighting.
  • Outlook Complexity: Delivering to Outlook presents unique challenges due to its intricate filtering mechanisms.
  • Admin Access: Administrative access is often needed to view spam filter reports and settings.
  • Tool Expertise: Select testing and analysis tools that align with your technical expertise.
  • Dynamic Filters: Spam filters evolve continuously, requiring ongoing monitoring and testing.

What email marketers say
9Marketer opinions

Identifying a company's spam filter involves several techniques. MXToolbox helps by revealing mail servers and filtering services through domain name analysis. Analyzing SPF, DKIM, and DMARC records provides insights into authentication practices. Bounce messages (NDRs) contain details about filtering mechanisms. Tools like GlockApps and Litmus test deliverability and identify spam filter triggers. Blacklist checks via Snov.io and IP reputation monitoring with Mailjet can reveal potential issues. Seed list testing, as suggested by Gmass, shows which providers filter emails as spam. Finally, SendPulse offers email testing to identify deliverability and spam triggers.

Key opinions

  • MXToolbox: MXToolbox can identify mail servers and filtering services by analyzing domain names.
  • Authentication Records: Analyzing SPF, DKIM, and DMARC records can reveal email authentication practices and potential spam filters.
  • Bounce Messages: Bounce messages (NDRs) provide information about spam filtering mechanisms.
  • Deliverability Testing: GlockApps and Litmus test email deliverability and identify spam filter triggers.
  • Blacklist Checks: Snov.io offers tools for blacklist checks to identify potential spam filtering issues.
  • IP Reputation: Mailjet monitors IP reputation, revealing potential spam filter triggers.
  • Seed Lists: Gmass suggests seed list testing to identify providers filtering emails as spam.
  • Email Testing Tools: SendPulse offers email testing tools to check deliverability and identify spam triggers.

Key considerations

  • Multiple Techniques: A combination of techniques provides the most comprehensive understanding of a company's spam filtering practices.
  • Tool Variety: Various tools exist for testing and analysis; select the ones that best fit your needs and technical expertise.
  • Dynamic Filters: Spam filters are constantly evolving, so regular monitoring and testing are essential.
  • False Positives: Deliverability testing may trigger false positives; interpret results cautiously.
Marketer view

Email marketer from EmailToolTester explains that GlockApps can be used to test email deliverability and identify spam filters. It sends emails to various mailboxes and provides reports on placement in inbox, spam folder, or missing status.

June 2022 - EmailToolTester
Marketer view

Email marketer from Gmass shares that setting up seed list testing involves sending test emails to a variety of email addresses across different providers. The results can indicate which providers are filtering your emails as spam.

February 2024 - Gmass
Marketer view

Email marketer from Reddit shares that analyzing a domain's SPF, DKIM, and DMARC records can provide insights into their email authentication practices and the potential spam filters they employ. Use online tools to check these records and understand their configuration.

April 2023 - Reddit
Marketer view

Email marketer from Litmus shares that Litmus provides email testing tools that can help identify potential deliverability issues and spam filter triggers. Their platform offers insights into how emails are rendered and filtered by different email clients and spam filters.

December 2021 - Litmus
Marketer view

Email marketer from SendPulse shares that their email testing tools enable users to check the deliverability of their emails and identify potential spam filter triggers before sending campaigns. The tool provides insights into spam score, authentication issues, and content-related problems.

March 2023 - SendPulse
Marketer view

Email marketer from Snov.io explains that using blacklist checking tools can reveal if a domain or IP address is listed on various blocklists, indicating potential spam filtering issues. Tools like MultiRBL and Blacklist Check can be used for this purpose.

January 2024 - Snov.io
Marketer view

Email marketer from Mailjet shares that monitoring IP reputation is crucial for identifying spam filtering issues. Services like Sender Score and Return Path's Sender Score can provide insights into IP reputation and potential spam filter triggers.

May 2023 - Mailjet
Marketer view

Email marketer from Neil Patel explains that MXToolbox can be used to identify the mail servers and potential spam filters a company is using. By entering the domain name, you can view the MX records, which often indicate the email service provider and associated filtering services.

December 2023 - Neil Patel
Marketer view

Email marketer from Stack Overflow shares that analyzing bounce messages (NDRs) can reveal information about the spam filtering mechanisms in place. The bounce message headers often contain details about the filtering software and policies.

September 2023 - Stack Overflow

What the experts say
4Expert opinions

Identifying a company's spam filter involves several investigative steps. Examining rejection messages and their SMTP logs, as well as MX records and IP ownership, can reveal the filters in use. When blocked, check error messages and associated URLs for details from blocklist operators. Seed lists are useful for delivery monitoring, but their results lack statistical significance and should include diverse seeds from multiple providers. Dealing with Outlook's delivery can be particularly challenging due to its complex and often opaque filtering mechanisms.

Key opinions

  • Rejection Analysis: Google rejection messages and analyze SMTP logs to find clues about the spam filter being used.
  • Infrastructure Checks: Check MX records and IP ownership to identify the mail servers and potential filtering services.
  • Blocklist Information: If blocked, review error messages and URLs provided by blocklist operators for details.
  • Seed List Limitations: Seed lists are helpful but limited; ensure diversity in seed selection and consider multiple providers.
  • Outlook Complexity: Outlook's delivery is complex and often inexplicable, posing unique challenges.

Key considerations

  • Combine Methods: Use a combination of methods to gain a comprehensive understanding of a company's spam filtering practices.
  • Error Message Specificity: Error messages vary in detail; some may require additional investigation.
  • Statistical Significance: Seed list results should be interpreted cautiously due to limited statistical significance.
  • Provider Relationships: Different seed providers have varying relationships with mailbox providers, affecting seed weighting.
  • Outlook Nuances: Delivering to Outlook may require specific strategies due to its unique challenges.
Expert view

Expert from Email Geeks shares that when you get rejections you can google the messages. They’re often distinctive. They also shares they tend to lookup the MX; it’s often obvious from there. If not, check the IP ownership of the MX servers.

June 2023 - Email Geeks
Expert view

Expert from Word to the Wise explains that seed lists can be a helpful part of your delivery monitoring, but they aren't the only thing to use. Seed list results are not statistically significant (you usually have very few seeds per domain). You want a variety of seeds, including different geographies and business types. Different seed providers weight seeds differently based on their relationship with mailbox providers. There are benefits to using different providers.

September 2022 - Word to the Wise
Expert view

Expert from Spam Resource explains that if you are being blocked, start by checking the error message. Look at the SMTP logs to see the exact error. If the errors include a URL, visit it to see what the blocklist operator says about the block. If the error is vague, try to connect with a mail client and send a test message, to see if more details emerge.

July 2023 - Spam Resource
Expert view

Expert from Email Geeks explains that Outlook is a giant black box of lack of support and intricate and inexplicable delivery.

October 2021 - Email Geeks

What the documentation says
6Technical articles

Identifying a company's spam filter involves understanding the filtering techniques used by major email security providers. Exchange Online Protection (EOP) utilizes connection filtering, spam signature filtering, and heuristic analysis, with admin reports available. Spamhaus maintains blocklists identifying spam sources. Gmail employs machine learning and provides admin reports. Cisco ESA uses reputation, content, and outbreak filters. Barracuda Spam Firewall uses real-time intent analysis, Bayesian filtering, and sender reputation. Proofpoint Email Protection uses a multi-layered approach with reputation, content, and threat analysis. Each system provides admins with customization and reporting options.

Key findings

  • EOP Techniques: Exchange Online Protection (EOP) employs connection, signature, and heuristic filtering.
  • Spamhaus Blocklists: Spamhaus maintains blocklists to identify spam sources.
  • Gmail ML: Gmail uses machine learning algorithms for spam filtering.
  • Cisco ESA: Cisco ESA uses reputation, content, and outbreak filters.
  • Barracuda Methods: Barracuda uses real-time intent, Bayesian, and sender reputation analysis.
  • Proofpoint Layers: Proofpoint uses reputation, content, and threat analysis in a multi-layered approach.

Key considerations

  • Admin Access: Administrative access is often required to view spam filter reports and settings.
  • Diverse Techniques: Spam filters use a variety of techniques, including reputation, content, and connection analysis.
  • Machine Learning: Modern email systems increasingly rely on machine learning for spam detection.
  • Customization: Administrators can often customize filtering policies based on organizational needs.
  • Regular Reporting: Regular review of spam filter reports is essential for maintaining email security.
Technical article

Documentation from Spamhaus explains that Spamhaus maintains various blocklists (e.g., SBL, XBL, PBL) that identify IP addresses and domains known for sending spam. Checking whether a company's mail server IP is listed on these blocklists can indicate the use of Spamhaus filtering.

June 2021 - Spamhaus
Technical article

Documentation from Cisco explains that the Cisco Email Security Appliance (ESA) uses various techniques such as reputation filtering, content analysis, and outbreak filters to identify and block spam. Admins can configure and monitor spam filtering policies through the ESA interface.

July 2023 - Cisco
Technical article

Documentation from Proofpoint explains that their Email Protection service uses a multi-layered approach including reputation analysis, content analysis, and advanced threat detection to identify and block spam and malicious emails. Administrators can access reports and customize policies.

May 2024 - Proofpoint
Technical article

Documentation from Google Workspace Admin Help explains that Gmail uses sophisticated machine learning algorithms to identify and filter spam. Admins can customize spam filter settings and view reports in the Google Admin console.

February 2025 - Google Workspace Admin Help
Technical article

Documentation from Barracuda explains that the Barracuda Spam Firewall uses techniques like real-time intent analysis, Bayesian filtering, and sender reputation to identify and block spam. Admins can customize filtering policies and view detailed reports.

February 2024 - Barracuda Networks
Technical article

Documentation from Microsoft Learn explains that Exchange Online Protection (EOP) uses various spam filtering techniques, including connection filtering, spam signature filtering, and heuristic analysis, to identify and block spam. Admins can view spam filter reports in the Security & Compliance Center.

October 2024 - Microsoft Learn