What causes Cloudmark trap hits and how can they be resolved?
Michael Ko
Co-founder & CEO, Suped
Published 26 Apr 2025
Updated 16 Aug 2025
5 min read
Dealing with Cloudmark trap hits can be a frustrating experience for any email sender. It often feels like you are caught in a cycle, especially if you have previously maintained good sending practices. These trap hits indicate that your email sending practices have likely triggered a detection mechanism, and the repercussions can significantly impact your email deliverability.
Cloudmark, now part of Proofpoint, operates a highly influential blacklist (or blocklist) known as Cloudmark Sender Intelligence (CSI). Getting listed on CSI can cause significant deliverability issues, leading to bounces and messages landing in the spam folder.
What are Cloudmark traps and why do they matter?
Cloudmark Sender Intelligence (CSI) is a reputation-based blocklist (blacklist) service that identifies and blocks IP addresses and domains associated with sending spam, phishing, and other malicious email. Its effectiveness comes from its sophisticated spam trap network and real-time threat detection, which contribute to its significant impact on email deliverability.
Spam traps are a core component of this system. These are email addresses designed not to receive legitimate mail but rather to catch spammers. When an email is sent to one of these addresses, it signals that the sender is likely using poor list acquisition or management practices. Understanding what spam traps are and how they work is crucial for maintaining good sender reputation.
Cloudmark evaluates many factors when assigning an IP address or domain a poor or suspect reputation. While hitting a single spam trap might not immediately result in a listing, consistent or numerous hits will almost certainly lead to your IP or domain being placed on their blocklist (blacklist). This means your emails will be rejected by mail servers that rely on Cloudmark's data, causing significant delivery failures.
Primary causes of Cloudmark trap hits
The most common reason for Cloudmark trap hits is poor list management. This includes using purchased or scraped email lists, which often contain invalid or old addresses that have been converted into spam traps. Sending to an old, unengaged list can also lead to trap hits, as previously valid addresses may have become recycled spam traps over time.
Another significant cause stems from your acquisition process. If you have webforms without proper spam protection, such as reCAPTCHA, bots can submit fake or malicious email addresses that turn into spam traps. A sudden influx of new contacts, particularly from these unprotected forms, can directly correlate with an increase in complaints and spam trap hits.
Technical issues can also contribute to listings. This might include mail server configuration problems, such as missing or incorrect reverse DNS (rDNS) records. Sometimes, a compromised server infected with malware can send out unwanted emails, leading to blocklist (blacklist) placements without your knowledge.
While less common, some recipient servers may have specific policies that trigger Cloudmark issues. These issues are often indicated in the SMTP error messages you receive. For a deeper dive into common causes of Cloudmark problems, you can refer to this article on Cloudmark issues.
Bad practices
Purchased lists: Acquiring email lists from third parties, which often contain spam traps.
Scraping addresses: Collecting emails from websites, which can lead to invalid addresses.
Outdated lists: Sending to old lists where previously valid addresses may have become traps.
No webform protection: Allowing bots to submit fake email addresses via unprotected signup forms.
Good practices
Organic acquisition: Building your list through legitimate sign-ups.
Regular cleaning: Removing unengaged subscribers and invalid addresses regularly.
Double opt-in: Requiring subscribers to confirm their email address.
Webform security: Implementing reCAPTCHA or similar tools to prevent spam submissions.
Strategies to resolve and prevent trap hits
Resolving Cloudmark trap hits requires a multi-faceted approach, starting with identifying the exact dates and campaigns that triggered the incidents. If you suspect an accidental send to an old list, immediately segment and cease sending to that portion of your audience. This helps prevent further damage.
Aggressive list cleaning is paramount. Regularly remove inactive or unengaged subscribers from your lists. Implement a double opt-in process for all new subscribers to verify their authenticity and ensure they genuinely want your emails. This preventative measure is highly effective in avoiding future spam trap encounters.
Proactive list hygiene
Regularly remove: Subscribers who haven't opened or clicked in a long time.
Implement double opt-in: For all new sign-ups to confirm interest.
Process bounces: Quickly remove hard bounces from your list.
Monitor acquisition channels: Add CAPTCHA to webforms to prevent bot sign-ups.
From a technical standpoint, ensure your mail server configurations are correct. This includes checking your reverse DNS (PTR) records, which should correctly resolve to your sending IP. If your server was compromised, addressing that security breach is critical. You also need to confirm that your SPF, DKIM, and DMARC records are properly configured.
Check your PTR recordBASH
dig -x 192.0.2.1 +short
Lastly, proactive blocklist (blacklist) monitoring is essential. Tools that monitor your IP and domain against major blocklists, including Cloudmark CSI, can alert you quickly to new listings. This allows for immediate action and helps prevent extended periods of deliverability issues. Knowing how email blacklists work is key to effective remediation.
Views from the trenches
Best practices
Regularly audit your email list for engagement and remove inactive subscribers.
Implement double opt-in for all new email sign-ups to ensure consent.
Utilize CAPTCHA or reCAPTCHA on webforms to prevent bot submissions.
Common pitfalls
Sending to purchased or scraped email lists, which are high-risk for spam traps.
Ignoring inactive subscribers, as old email addresses can become recycled traps.
Not monitoring webform submissions for suspicious or bot-generated addresses.
Expert tips
Focus on the root cause: Most trap hits stem from list acquisition or hygiene.
Segment your audience: Send to engaged users to reduce risk.
Monitor your reputation consistently to catch issues early.
Expert view
Expert from Email Geeks says understanding how addresses are acquired is key to resolving trap hits.
2022-06-24 - Email Geeks
Marketer view
Marketer from Email Geeks says sudden spikes in Cloudmark trap hits can occur even with clean acquisition, possibly due to sending to older, unengaged lists.
2022-06-24 - Email Geeks
The path to better deliverability
Cloudmark trap hits are a clear signal that your email sending practices require immediate attention. They are a direct result of poor list management, flawed acquisition processes, or underlying technical issues. Ignoring these signals can lead to severe and prolonged deliverability problems, affecting your ability to reach your audience effectively.
The path to resolution involves a combination of diligent list hygiene, securing your email acquisition channels, and ensuring your technical configurations are flawless. This proactive approach not only helps you recover from current blocklistings but also builds a resilient sending reputation that protects your future email campaigns.
By focusing on these areas, you can significantly reduce the risk of Cloudmark trap hits and maintain consistent inbox placement for your legitimate emails. This ensures your messages reach their intended recipients, supporting your communication goals effectively.
Cloudmark CSI, can alert you quickly to new listings. This allows for immediate action and helps prevent extended periods of deliverability issues. Knowing how email blacklists work is key to effective remediation.
