Summary
Identifying which major Mailbox Providers (MBPs) use Cloudmark for spam filtering is complex due to a combination of factors: Cloudmark's confidentiality policies, the integration of Cloudmark with other filtering systems, the use of reseller agreements by smaller ISPs, and the dynamic nature of spam filtering solutions. While Comcast is a known user, along with indications of usage by Charter, Cox, and Roadrunner, many providers combine Cloudmark with in-house or other third-party solutions like Vade or Synacor. Proofpoint, Cloudmark's parent company, offers wider email security solutions used by various MBPs. Analyzing email headers for 'X-Cloudmark-Analysis' or monitoring reputation for Cloudmark blocks can provide clues. Ultimately, focusing on strong email authentication (SPF, DKIM, DMARC) and deliverability best practices is crucial, regardless of the specific spam filter in use.
Key findings
- Confirmed Cloudmark Users: Comcast is a confirmed user of Cloudmark. Charter, Cox, and Roadrunner show recent indications of Cloudmark use in some tests.
- European ISPs: Some European ISPs, including Tiscali.it, Libero.it, TalkTalk.co.uk, and Bluewin.ch, appear to use Cloudmark.
- Indirect Integration: Smaller ISPs often integrate Cloudmark through reseller agreements, making comprehensive tracking difficult.
- Combined Solutions: Most MBPs use Cloudmark in combination with other spam filtering techniques (in-house or third-party).
- Cloudmark Client List: Cloudmark does not disclose its client list due to confidentiality agreements.
- Proofpoint's Role: Proofpoint's email security suite, powered by Cloudmark technology, is used by various MBPs without directly identifying them.
- Cloudfilter MX Records: Domains with *.<http://cloudfilter.net|cloudfilter.net> as their MX record are likely using Cloudmark.
Key considerations
- Configuration Matters: Cloudmark's effectiveness is highly dependent on its specific configuration and integration by each MBP.
- Header Analysis: Analyzing email headers for 'X-Cloudmark-Analysis' can provide evidence of Cloudmark use.
- Reputation Monitoring: Reputation monitoring services can help identify IP addresses being blocked by Cloudmark.
- SPF, DKIM, DMARC: Implementing strong email authentication (SPF, DKIM, DMARC) is critical, regardless of the specific spam filter used.
- Dynamic Environment: The email filtering landscape is constantly evolving, making it difficult to maintain an up-to-date list of Cloudmark users.
- Bounce Message Analysis: Analyzing bounce messages may offer clues about the filtering services in use.
What email marketers say
12 marketer opinions
Identifying which Mailbox Providers (MBPs) use Cloudmark for spam filtering is complex. While some MBPs like Comcast are known Cloudmark users, many others integrate it via reseller agreements or combine it with in-house solutions, making a comprehensive list difficult to obtain. Checking email headers for 'X-Cloudmark-Analysis' can offer clues. Ultimately, focusing on email authentication (SPF, DKIM, DMARC) and deliverability best practices is crucial, irrespective of the specific filtering system used.
Key opinions
- Known Cloudmark Users: Comcast is a known user of Cloudmark for spam filtering. Charter, Cox, and Roadrunner have shown evidence of Cloudmark usage in tests.
- Regional Variations: In Europe, ISPs like Tiscali.it, Libero.it, TalkTalk.co.uk, and Bluewin.ch appear to use Cloudmark.
- Indirect Integration: Many smaller ISPs integrate Cloudmark through reseller agreements.
- Combination of Solutions: Most MBPs use Cloudmark in combination with other spam filtering techniques, including in-house solutions.
- Proofpoint's Role: Proofpoint, Cloudmark's parent company, offers broader email security solutions used by many large organizations and ISPs.
- Cloudfilter MX records: If a domain has *.<http://cloudfilter.net|cloudfilter.net> as the MX then they are definitely using Cloudmark.
Key considerations
- Header Analysis: Examine email headers for 'X-Cloudmark-Analysis' to identify potential Cloudmark usage.
- Dynamic Landscape: The landscape of spam filtering solutions changes frequently, making it difficult to maintain an accurate list of Cloudmark users.
- Authentication Importance: Implementing SPF, DKIM, and DMARC is critical for email deliverability, regardless of the specific spam filter in use.
- Reputation Monitoring: Reputation monitoring services may provide insights into IP addresses being blocked by Cloudmark.
- bounce message analysis: Analyzing bounce messages can help identify possible clues to which filtering services are being used.
Marketer view
Marketer from Email Geeks indicates that in Europe, the list of ISPs using cloudmark appears to include <http://Tiscali.it|Tiscali.it>, <http://Libero.it|Libero.it>, <http://TalkTalk.co.uk|TalkTalk.co.uk>, <http://Bluewin.ch|Bluewin.ch>, etc.
22 Apr 2022 - Email Geeks
Marketer view
Email marketer from StackExchange explains that determining which specific mailbox providers use Cloudmark directly is difficult due to proprietary implementation. Suggests analysing bounce messages for possible clues.
24 Feb 2025 - StackExchange
What the experts say
3 expert opinions
Identifying specific Mailbox Providers (MBPs) using Cloudmark is complex, and its effectiveness is heavily dependent on integration and configuration. Comcast is identified as a user, while Spectrum and Optimum may utilize Synacor. Reputation monitoring can indirectly indicate Cloudmark usage by identifying blocking patterns.
Key opinions
- Comcast's Use of Cloudmark: Comcast is confirmed to be using Cloudmark for spam filtering.
- Spectrum and Optimum: Spectrum and Optimum's MX records suggest they might be using Synacor as a filtering solution, not necessarily Cloudmark.
- Cloudmark Effectiveness: Cloudmark's performance is heavily reliant on its specific configuration and integration within the MBP's overall filtering system.
- Indirect Identification: Reputation monitoring can indirectly indicate Cloudmark usage if a provider's IPs are frequently blocked by Cloudmark.
Key considerations
- Configuration Matters: The effectiveness of Cloudmark varies significantly based on how each MBP configures and integrates it.
- Indirect Detection: Directly identifying Cloudmark usage may be difficult, making reputation monitoring a useful, though indirect, method.
- Filtering Solutions: MBPs can use a variety of filtering solutions - Cloudmark is one option, but others like Synacor are also deployed.
Expert view
Expert from Spam Resource notes that Cloudmark's effectiveness depends on its configuration and how well it's integrated with other filtering systems by the MBP.
26 Oct 2023 - Spam Resource
Expert view
Expert from Word to the Wise explains monitoring services may identify when an IP address is being blocked by Cloudmark, indicating that a provider using Cloudmark may be filtering messages from that IP.
20 Mar 2023 - Word to the Wise
What the documentation says
5 technical articles
Cloudmark provides anti-spam solutions to numerous ISPs and messaging providers, but keeps their client list confidential. Proofpoint integrates Cloudmark technology into its email security suite, used by various mailbox providers. Email header fields can sometimes reveal the filtering services used by an ISP. Employing strong email authentication methods like DKIM and SPF is crucial for deliverability, irrespective of the specific spam filter used.
Key findings
- Client Confidentiality: Cloudmark does not publicly disclose its customer list due to confidentiality reasons.
- Proofpoint Integration: Proofpoint's email security suite, which includes Cloudmark technology, is used by multiple mailbox providers.
- Header Information: Email header fields may provide clues about the spam filtering services in use by an ISP.
- DKIM Importance: DKIM is an essential email authentication method that helps prevent email spoofing and is important for passing through spam filters.
- SPF Importance: SPF records help to control which servers can send email for your domain, crucial for deliverability.
Key considerations
- Indirect Identification: Directly identifying Cloudmark users is challenging, as Cloudmark does not disclose this information.
- Holistic Security: Proofpoint's broader email security suite suggests a more comprehensive approach to email filtering than just Cloudmark alone.
- Authentication Focus: Prioritizing strong email authentication practices (DKIM, SPF) is essential for good deliverability, regardless of the filters used by MBPs.
- Investigate Headers: Take the time to investigate email headers for clues as to the filters the ISPs might be using to filter spam.
Technical article
Documentation from IETF explains that SPF records are very important for your domain because they specify the mail servers allowed to send email on behalf of your domain. Filtering services can utilise this information when receiving emails from your servers.
6 Jul 2022 - IETF
Technical article
Documentation from DKIM.org explains that DKIM is a very important email authentication method that helps prevent email spoofing - passing through email filters like Cloudmark depends on it.
16 Mar 2024 - DKIM.org
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