Why is my IP address listed on Cloudmark CSI-Global?
Matthew Whittaker
Co-founder & CTO, Suped
Published 31 Jul 2025
Updated 15 Aug 2025
7 min read
Getting an email bounced with a Cloudmark CSI-Global listing message is a clear sign your email deliverability is in trouble. It means that Cloudmark, a significant player in anti-spam technology, has flagged the IP address your emails are originating from as a source of undesirable traffic. When this happens, your legitimate emails may fail to reach their intended recipients, getting blocked entirely or routed directly to spam folders.
The message often looks like a soft bounce, indicating that the recipient system isn't accepting network messages because your IP is listed on Cloudmark CSI-Global. This isn't just a minor inconvenience, it can severely impact your ability to communicate effectively, whether for transactional emails, marketing campaigns, or even personal correspondence.
Understanding why your IP address landed on this blocklist (or blacklist) is the first step toward resolution. Cloudmark's Sender Intelligence (CSI) uses real-time data to build sender reputations, and a listing suggests a detected issue with your sending practices or server configuration.
What is Cloudmark CSI-Global?
Cloudmark CSI-Global is a real-time IP reputation service. It leverages data from Cloudmark's Global Threat Network™ to identify IP addresses that are sources of spam, phishing, and other malicious email activity. Mail servers, internet service providers (ISPs), and organizations worldwide subscribe to CSI to filter out unwanted email traffic, protecting their users from threats.
Essentially, it acts as a gatekeeper. If your IP address has a poor reputation on Cloudmark CSI, inbound mail servers using this service will refuse connections or reject emails coming from that IP. This preventative measure helps reduce the volume of spam hitting inboxes globally.
Cloudmark prides itself on the accuracy of its data, which is constantly updated based on observed email streams. If you encounter a bounce message referencing Cloudmark CSI-Global, it means their system has detected activity from your IP that aligns with their criteria for poor sender reputation. You can often find general information about why IPs are listed on the Cloudmark Sender Intelligence FAQ page.
Reasons for a Cloudmark CSI-Global listing
Several factors can lead to your IP address being listed on Cloudmark CSI-Global. The most common reasons revolve around the quality and nature of your email sending. High volumes of user complaints (spam reports) or hitting spam traps are significant indicators to Cloudmark's system that an IP is sending unsolicited mail. Even if your emails are transactional, complaints can still occur if recipients don't recognize the mail or find it unwanted.
Beyond direct spamming, technical misconfigurations play a role. Issues like missing or incorrect reverse DNS (rDNS) records, open relays, or other server vulnerabilities can also trigger a listing. Cloudmark uses a comprehensive approach, combining behavioral analysis with technical checks to assess an IP's reputation.
Sometimes, the issue isn't directly your fault. If you're using a shared IP address, the sending habits of other users on that same IP can negatively affect your reputation. Even if your sending practices are impeccable, another sender on the same IP could cause it to be blocklisted (or blacklisted). This highlights the importance of understanding your IP environment.
Common technical issues
Missing reverse DNS: An IP without a proper rDNS record looks suspicious.
Open relays: Misconfigured servers that allow unauthorized third parties to send mail through them.
Compromised accounts: If an email account on your server is hacked and used to send spam.
Generic rDNS: IP addresses with generic rDNS (e.g., from a hosting provider) can sometimes be seen as less reputable until they establish a history.
How to diagnose and address the issue
When you receive a bounce message indicating a Cloudmark CSI-Global listing, the first step is to confirm the listing and understand its context. The bounce message itself usually provides the specific IP address that is listed. For example, a bounce might state something similar to: "5.3.2 (system not accepting network messages) [IP address] is listed on Cloudmark CSI-Global."
You can visit the Cloudmark Sender Intelligence (CSI) portal, often linked directly in the bounce message, to check the status of your IP and potentially request delisting. This portal is the primary mechanism for interaction with Cloudmark regarding IP reputation.
While a quick delisting might resolve the immediate problem, it's crucial to identify the underlying cause to prevent recurrence. This involves reviewing your email logs, checking for unusual sending patterns, verifying your email authentication records (SPF, DKIM, DMARC), and ensuring your mailing lists are clean and permission-based. For example, ensuring your Microsoft 365 or Google Workspace configurations are correct is vital to avoid issues.
Example Cloudmark CSI bounce message
5.3.2 (system not accepting network messages) p-impin015.msg.pkvw.co.charter.net cmsmtp 13.111.125.163 is listed on Cloudmark CSI-Global. Please visit https://csi.cloudmark.com/en/reset?ip=13.111.125.163 AUP#In-1200
Immediate action
Delisting request: Submit a request through the Cloudmark CSI portal to delist your IP address. This can sometimes result in an auto-delisting for minor offenses.
Review logs: Check your mail server logs for any unusual activity or unexpected email volumes.
Temporary IP change: If possible and urgent, consider temporarily switching to a different sending IP.
Address shared IP issues: If on a shared IP, contact your hosting provider to investigate other users' activity or request a dedicated IP.
Long-term prevention
List hygiene: Regularly clean your email lists, removing inactive or invalid addresses to prevent hitting spam traps. Learn about what spam traps are.
Sender authentication: Implement and monitor SPF, DKIM, and DMARC. Proper authentication builds trust with ISPs.
Feedback loops: Sign up for ISP feedback loops to receive reports on user complaints, allowing you to quickly remove disengaged subscribers.
Preventing your IP address from being listed on Cloudmark CSI-Global, or any other blocklist (or blacklist), requires a proactive approach to email deliverability. It's not just about getting delisted, but ensuring you maintain a clean sending reputation. Consistent adherence to email best practices is paramount.
One of the most critical aspects is managing your email list. Only send to recipients who have explicitly opted in to receive your emails. Regularly cleaning your lists by removing inactive or unengaged subscribers helps avoid hitting spam traps and reduces complaint rates. Remember, even transactional emails can lead to complaints if not managed properly.
Proper email authentication is non-negotiable. Configuring and maintaining accurate SPF, DKIM, and DMARC records signals to receiving mail servers that your emails are legitimate and haven't been tampered with. These records help establish trust and are crucial for good inbox placement. You can refer to a simple guide to DMARC, SPF, and DKIM.
Lastly, continuous monitoring of your IP and domain reputation is essential. Regularly checking common blocklists and actively reviewing your email bounce logs can alert you to issues before they escalate into widespread deliverability problems. Being listed on a blocklist like Cloudmark CSI (or even other significant ones like CBL) means your emails aren't reaching their destination, highlighting the need for vigilance.
Factor
Description
Impact on listing
Sending volume
Sudden spikes in sending or very low volumes.
High volume can trigger filters, low volume struggles to build reputation.
Recipient engagement
How recipients interact with your emails (opens, clicks, complaints).
Low engagement and high complaints are strong indicators of poor reputation.
Email content
Spammy content, broken links, or misleading information.
Content matching spam patterns will quickly lead to listings.
DNS records
Proper configuration of SPF, DKIM, DMARC, and rDNS.
Misconfigured or missing records severely harm trust and lead to blocks.
Shared IP neighbors
Activity of other senders sharing your IP address.
Poor sending by others on a shared IP can inadvertently blacklist your IP.
Proactive reputation management
Implement feedback loops: These directly inform you of spam complaints, allowing you to remove complaining users from your list quickly.
Monitor bounce rates: High bounce rates, especially hard bounces, can indicate a poor list quality and lead to blocklistings.
Warm-up new IPs: If you're using a new IP, gradually increase sending volume to build a positive reputation.
Maintain opt-in lists: Ensure all recipients have given explicit permission to receive emails.
Views from the trenches
Best practices
Regularly audit your sending infrastructure for any vulnerabilities or misconfigurations that could be exploited by spammers.
Focus on building strong relationships with your subscribers to minimize spam complaints and foster positive engagement.
Leverage real-time monitoring tools to track your IP's reputation across various blacklists and respond immediately to new listings.
Common pitfalls
Overlooking the impact of shared IP addresses, where other users' poor sending practices can unfairly affect your deliverability.
Neglecting to implement or correctly configure email authentication protocols, which are crucial for establishing sender trust.
Failing to regularly clean and segment email lists, leading to higher bounce rates and increased risk of hitting spam traps.
Expert tips
Implement a clear opt-in process for all subscribers to ensure consent and reduce the likelihood of spam complaints.
Analyze your bounce messages thoroughly to understand the specific reasons for rejections, not just the fact of a bounce.
Engage with Cloudmark's remediation process promptly and provide all requested information to facilitate faster delisting.
Expert view
Expert from Email Geeks says: "Your IP has been listed on Cloudmark CSI-Global, and you are being blocked based on that. Following the link allows you to ask Cloudmark to delist you."
March 11, 2020 - Email Geeks
Expert view
Expert from Email Geeks says: "Cloudmark may list based on user complaints or spam traps, so you should review your list sources and the expectations your users have to prevent it from recurring."
March 11, 2020 - Email Geeks
Moving forward after a Cloudmark CSI-Global listing
Being listed on Cloudmark CSI-Global, or any blocklist (sometimes called a blacklist), can be frustrating, but it's a manageable situation. The key is to act swiftly and methodically, not just to get delisted, but to implement changes that prevent future occurrences. This process typically involves a combination of immediate remediation and long-term strategic adjustments to your email program.
Once delisted, commit to ongoing vigilance. Regular monitoring of your sender reputation, combined with meticulous list hygiene and strong email authentication, will fortify your deliverability. Think of it as an ongoing health check for your email program, similar to how you'd regularly check if your IP address is blacklisted when sending email.
Ultimately, maintaining a positive sender reputation is about sending valuable content to engaged recipients. By focusing on consent, relevance, and technical correctness, you can minimize your risk of future Cloudmark CSI-Global listings and ensure your emails consistently reach the inbox.
Microsoft 365 or 
Google Workspace configurations are correct is vital to avoid issues.
