What is the difference between Cloudmark Authority and Cloudmark Sender Intelligence (CSI)?

Cloudmark Authority is their core content filtering engine, which analyzes email content for spam, phishing, and malware characteristics. Cloudmark Sender Intelligence (CSI) is a real-time blacklist of IP addresses and domains with poor sending reputations. Both work in tandem to provide comprehensive email security.

What happens if my email is flagged by Cloudmark or listed on CSI?

If your IP or domain is listed on Cloudmark CSI, it means Cloudmark's system has detected problematic sending behavior. This can lead to your emails being blocked or routed to the spam folder by any Mailbox Provider (MBP) or ISP that utilizes Cloudmark's filtering services. You may experience reduced deliverability rates to affected providers.

How can I check if my IP or domain is listed by Cloudmark?

You can check if your IP address is listed on Cloudmark CSI by visiting their official CSI lookup portal. For domains, while a direct public lookup might not be as common, you should monitor your overall domain reputation and respond to any deliverability issues from Cloudmark-using providers.

What steps can I take to improve my email deliverability with Cloudmark-protected providers?

To improve your standing with Cloudmark, focus on maintaining a clean email list, ensuring proper email authentication (SPF, DKIM, DMARC), and sending valuable, engaging content to your subscribers. If you are listed on CSI, follow their delisting process after addressing the root cause of the listing.

Which major Mailbox Providers (MBPs) use Cloudmark for spam filtering? - Technical - Email deliverability - Knowledge base

Understanding which major Mailbox Providers (MBPs) use Cloudmark for spam filtering is crucial for anyone involved in email marketing or deliverability. Cloudmark is a significant player in the email security landscape, providing anti-spam, anti-phishing, and anti-malware solutions to a wide range of organizations, including many large internet service providers (ISPs) and mailbox providers.

Their technology often forms a key layer in how email is filtered before it reaches an end-user's inbox. If your emails are consistently landing in spam folders, or if you're experiencing unexpected blockages, it's worth investigating if the receiving MBP utilizes Cloudmark's services, as this can provide valuable insights into the potential causes.

My goal is to shed light on some of the prominent providers that rely on Cloudmark, helping you better understand the landscape and optimize your email sending practices. Knowing this information can significantly impact your email deliverability strategies.

Understanding Cloudmark's role in filtering

Cloudmark plays a critical role in the email ecosystem by providing robust anti-spam and messaging security solutions. Their core product, Cloudmark Authority, is a content filtering engine that identifies and blocks unwanted emails across various messaging streams. It's known for its high accuracy in detecting spam, phishing, and malware, often achieving impressive rates with minimal false positives. This reputation has made it a preferred choice for many large network operators.

A key component of Cloudmark's system is Cloudmark Sender Intelligence (CSI). This is a real-time blacklist (or blocklist) of IP addresses and domains that have a poor sending reputation, often due to sending spam or exhibiting other abusive behaviors. When an IP address appears on the CSI blocklist, it can severely impact email deliverability to all MBPs that use Cloudmark's services. It's a comprehensive reputation-based approach to fighting unsolicited messages.

Many providers choose Cloudmark because of its global threat network, which gathers data from a vast array of sources to quickly adapt to new spam trends and phishing attempts. This collective intelligence helps keep their filtering effective against evolving threats, providing a strong line of defense for their users' inboxes. Their solutions are often implemented at the network level, influencing a large volume of email traffic.

Understanding Cloudmark Sender Intelligence (CSI)

CSI is an integral part of Cloudmark's filtering. If your sending IP is listed on CSI, it means Cloudmark's system has detected problematic sending behavior from that IP, leading to a negative reputation score. This can cause legitimate emails to be blocked or filtered into spam folders by any MBP that integrates with Cloudmark.

Regularly monitoring your IP reputation and ensuring compliance with best sending practices is essential to avoid being listed on such a critical email blacklist. Being proactive is always better than reacting to deliverability issues.

Key mailbox providers utilizing Cloudmark

Several major Mailbox Providers and Internet Service Providers (ISPs) have historically, or currently, use Cloudmark's spam filtering solutions. These typically include large regional and national providers that handle a significant volume of email traffic for their subscribers. The adoption of Cloudmark helps these organizations maintain a secure and clean email environment, reducing the burden of unwanted messages for their users.

While the exact list can change as providers update their systems or sign new contracts, some names frequently associated with Cloudmark include major U.S. cable and telecommunication companies, as well as several international providers. Keeping track of these affiliations is essential for senders to anticipate potential filtering behaviors and adapt their strategies accordingly.

Mailbox Provider/ISP	Domain Examples	Notes on Cloudmark Use
Comcast	comcast.net	A long-time user of Cloudmark's filtering services for their email infrastructure.
Charter (Spectrum)	spectrum.net	Spectrum, owned by Charter, has been identified as utilizing Cloudmark for filtering.
Cox	cox.net	Confirned by various reports and tests to use Cloudmark solutions.
Optimum	optimum.net	Often grouped with providers like Spectrum, indicating Cloudmark usage.
RoadRunner (TWC/Spectrum)	rr.com	Legacy domain, still uses Cloudmark Authority Email (CMAE).
EarthLink	earthlink.net	Listed as an early adopter of Cloudmark's solutions.
Rackspace	rackspace.com	A case study confirms Rackspace's use of Cloudmark for high accuracy.
Proofpoint	proofpoint.com (as a gateway)	Acquired Cloudmark in 2017, integrating its filtering technology.

It's important to note that while a provider might use Cloudmark, they may also employ additional layers of filtering or internal blacklists (or blocklists). This means that being listed on CSI isn't the only factor impacting your deliverability to these providers, but it's a very significant one. You can sometimes identify if a domain uses Cloudmark by checking their MX records for cloudfilter.net in the entry.

How Cloudmark's systems impact deliverability

Cloudmark's filtering goes beyond simple blocklist (or blacklist) lookups. They use a combination of advanced techniques to assess email legitimacy, including reputation-based filtering and real-time content analysis. Their system leverages a global network of sensors and user feedback to identify new spam and phishing campaigns as they emerge, allowing for rapid detection and blocking.

The collaborative filtering approach means that as users report spam, Cloudmark's system learns and updates its filters in real-time. This dynamic system makes it challenging for spammers to adapt and bypass filters, but it also means legitimate senders must maintain an excellent sending reputation to avoid being caught in the crossfire. A comprehensive overview of Cloudmark highlights these mechanisms.

It's important to remember that even if Cloudmark identifies an email as spam, it doesn't always guarantee immediate spam folder placement. Mailbox providers often use a multi-layered filtering approach, where Cloudmark is one of many signals considered. Other factors, such as sender authentication (SPF, DKIM, DMARC), recipient engagement, and internal policies, also play a significant role.

Reputation based filtering

IP/Domain Reputation: Cloudmark maintains databases of known good and bad sending IPs and domains. Your sending history, spam complaint rates, and engagement metrics directly influence your reputation.
Sender behavior: Sudden spikes in volume, sending to unknown users, or hitting spam traps can negatively impact your sender reputation.

Content based filtering

Message content: Cloudmark analyzes email content for spammy keywords, suspicious links, malformed HTML, and other characteristics commonly found in unwanted messages.
Pattern recognition: Their system uses advanced algorithms to identify patterns associated with spam and phishing across the global threat network.

Navigating Cloudmark blocklists and ensuring inbox placement

If your emails are being blocked or sent to the spam folder by MBPs using Cloudmark, it's essential to act quickly. The first step is to check your sending IP address and domain reputation. You can use a blocklist checker to see if you are listed on CSI or other major blacklists (or blocklists). Cloudmark provides an online portal for CSI lookups and delisting requests.

Beyond checking blocklists (or blacklists), review your email sending practices. Ensure your email lists are clean and regularly updated to avoid sending to invalid or unengaged addresses. High bounce rates and spam complaints are major red flags for any filtering system, including Cloudmark. Implement a double opt-in process for new subscribers to verify their consent.

Furthermore, ensure your email authentication records (SPF, DKIM, and DMARC) are correctly configured. These standards help mailbox providers verify that your emails are legitimate and prevent spoofing. A proper setup signals trustworthiness to filters like Cloudmark. If you believe you have been incorrectly listed, Cloudmark does provide channels to address content filtering issues.

Check MX records for cloudfilter.netbash

dig MX example.com

Views from the trenches

Best practices

Maintain a clean mailing list by regularly removing inactive or bouncing email addresses.

Implement a double opt-in process for all new subscribers to ensure explicit consent.

Monitor your sending reputation across major blacklists and Cloudmark CSI proactively.

Ensure SPF, DKIM, and DMARC records are correctly configured and aligned.

Segment your audience and send relevant content to minimize spam complaints.

Common pitfalls

Sending to purchased or old lists without re-engagement campaigns leads to high bounces and complaints.

Ignoring spam complaints or high spam trap hits will quickly tank your sender reputation.

Not authenticating your emails with SPF, DKIM, and DMARC makes you look suspicious to filters.

Over-sending or sending irrelevant content that leads to high unsubscribe rates.

Failing to monitor deliverability metrics and act on red flags from Postmaster Tools.

Expert tips

Set up feedback loops with MBPs to receive spam complaint data directly.

Warm up new IPs or domains slowly to build a positive sending history.

Regularly test your email content to identify potential spam triggers before sending.

Use a dedicated sending IP if you send high volumes to maintain better control over your reputation.

Engage with your audience to foster positive interactions and improve engagement metrics.

Expert view

Expert from Email Geeks says that Comcast has historically used Cloudmark, but some providers, like Spectrum, might be running Synacor as a primary filter, which might have its own aggressive filtering.

2022-01-07 - Email Geeks

Marketer view

Marketer from Email Geeks says that just because a content scanner like Cloudmark Authority Email determines mail to be spam, it does not always result in direct spam folder placement due to multi-layered filtering.

2022-01-07 - Email Geeks

Final thoughts on Cloudmark and email deliverability

Cloudmark remains a powerful and widely adopted solution for spam filtering among numerous major Mailbox Providers and ISPs globally. Its combination of reputation-based filtering and content analysis, bolstered by a vast threat network, makes it a formidable barrier against unwanted email.

For email senders, understanding Cloudmark's presence and its impact is vital for maintaining high deliverability rates. Proactive monitoring of your sending reputation, strict adherence to email best practices, and proper email authentication are key to navigating these sophisticated filters and ensuring your messages reach their intended recipients.