How do multi-tenant hosting IPs get listed on Spamhaus SBL?
Matthew Whittaker
Co-founder & CTO, Suped
Published 6 Jun 2025
Updated 18 Aug 2025
7 min read
Multi-tenant hosting environments, where numerous websites and services share the same server infrastructure and IP addresses, offer cost-effective solutions for many. However, this shared nature introduces unique challenges, especially when it comes to email deliverability. A significant concern for anyone operating within such a setup is the potential for their shared IP addresses to end up on reputable blocklists like the Spamhaus SBL (Spamhaus Block List).
The Spamhaus SBL is a critical blocklist (or blacklist) that lists IP addresses identified as sources of spam or other malicious activities. Its purpose is to help mail servers filter out unwanted email. When a multi-tenant IP gets listed, it can severely impact the email deliverability of all legitimate users on that shared IP, leading to bounced emails and significant reputation damage. It is crucial to understand why this happens and what steps can be taken to prevent or resolve such listings.
The core issue often stems from the actions of a single bad actor whose misuse of the shared resources can lead to collective punishment for everyone sharing the IP. This situation can be particularly frustrating for well-meaning businesses trying to maintain their email sending reputation.
In a multi-tenant hosting setup, multiple websites and email accounts operate from the same server and, crucially, often share a common pool of IP addresses for sending outgoing email. This arrangement is common with shared hosting providers and some smaller email service providers (ESPs).
The advantage for users is lower cost, as the infrastructure expenses are distributed among many tenants. However, the downside is that your email sending reputation becomes intertwined with that of your neighbors on the same IP. If one tenant engages in activities that trigger spam complaints or appear suspicious to email blocklists, the entire IP address, and by extension, all legitimate senders on it, can suffer the consequences. This is why you might suddenly find your emails going to spam or being rejected even if you maintain good sending practices yourself.
Understanding the difference between shared and dedicated IPs highlights why shared environments are more susceptible to broad blocklistings.
Spamhaus maintains several blocklists, and the SBL is specifically designed to list IP addresses that are observed sending spam or supporting spam operations. Spamhaus's criteria for SBL listings are intentionally broad to effectively combat various forms of email abuse.
For multi-tenant hosting IPs, a listing typically occurs due to one or more tenants on that shared IP engaging in activities that violate Spamhaus's policies. This could range from sending unsolicited bulk email (spam) to hosting malware, phishing sites, or acting as a command-and-control server for botnets. Spamhaus aggregates data from various sources, including spam traps, direct abuse reports, and threat intelligence. If enough evidence accumulates against an IP address, it will be added to the SBL. The Spamhaus blocklist policy explains their criteria in more detail.
A common scenario for shared IPs is what's sometimes called snowshoe spamming, where spammers distribute their unwanted mail across a large number of IP addresses to evade detection. If a multi-tenant IP is part of such a pool, even if you're not the one snowshoeing, your IP could still get swept into a blocklist due to association. It's an unfortunate reality of shared IP spaces, which is also a reason IPs and domains are suddenly entering blacklists.
The ripple effect of bad actors
When a single tenant on a multi-tenant IP engages in abusive email practices, the entire IP address can be listed on the Spamhaus SBL. This means that all legitimate email senders sharing that IP will experience delivery issues, regardless of their own sending hygiene. This impact of an IP blocklisting can be severe, leading to lost business and damaged reputation.
Proactive measures for hosting providers and tenants
Preventing an SBL listing on a multi-tenant IP requires a collaborative effort between the hosting provider and its tenants. Proactive measures are always more effective than reactive ones.
For hosting providers
Robust monitoring: Implement systems to constantly monitor IP reputation and detect suspicious sending patterns from individual tenants. Automated alerts for sudden spikes in spam complaints or bounce rates are essential.
Strict abuse policy: Enforce a clear, strict anti-spam policy with immediate action against abusers. This includes suspending or terminating accounts that engage in spamming.
IP segmentation: Segment IPs by customer type or sending volume. High-volume or new senders could be placed on IPs with stricter monitoring or separate IP pools to contain potential damage.
For tenants (email senders)
Maintain clean lists: Regularly clean your email lists, remove inactive subscribers, and promptly address bounces. Avoid purchasing or scraping email addresses.
Implement authentication: Ensure your domain is properly configured with SPF, DKIM, and DMARC. These records help verify your emails and reduce the likelihood of them being marked as spam. Read our simple guide to email authentication.
For individual users, it's also important to be aware of the hosting provider's practices. If your provider is not vigilant about abuse, you might find your email deliverability consistently suffering. In such cases, considering a switch to a provider with better email hygiene practices or a dedicated IP might be necessary.
Remediation and recovery
If a multi-tenant IP address you use gets listed on the Spamhaus SBL (or any other blocklist), immediate action is required to restore your email deliverability. This often involves a multi-step process.
Identify the cause: The first step is to determine why the IP was listed. Often, bounce messages will indicate an SBL listing, similar to the bounce error example from GoDaddy. If you're using a shared IP, contact your hosting provider or ESP to investigate. They should be able to identify the offending tenant or script.
Request de-listing: Once the source of the problem is resolved, either the hosting provider or the IP owner (depending on the listing type and Spamhaus's policy) must formally request de-listing from Spamhaus. This process requires demonstrating that the abuse has stopped and measures are in place to prevent recurrence. Learn more about how to resolve an SBL listing. Be aware that if your IP is repeatedly blocklisted, the de-listing process can become more difficult, as Spamhaus notes in its FAQs, especially for repeat offenders.
Monitor for re-listing: After de-listing, continuously monitor the IP's reputation. If the underlying issue (e.g., an uncontained spammer) is not fully resolved, the IP may be quickly re-listed. For a persistent issue, you might need to consider why your IP is repeatedly blocklisted.
Here's a common bounce message you might see if your email is rejected due to an SBL listing:
Example bounce messageplain
554 5.7.1 Service unavailable; Client host [X.X.X.X] blocked using Spamhaus SBL. IB104
Views from the trenches
Maintaining good email deliverability in a multi-tenant hosting environment requires diligence. While hosting providers bear the primary responsibility for managing their IP reputation, individual tenants also play a crucial role in preventing activities that could lead to blocklistings (or blacklistings).
Best practices
Actively vet new clients, especially those requiring high email volume, to ensure they adhere to anti-spam policies.
Implement automated systems to detect sudden changes in sending behavior or complaint rates for all shared IPs.
Communicate clearly with clients about acceptable email practices and the consequences of policy violations.
Maintain a clear process for handling abuse complaints and delisting requests with blocklist operators like Spamhaus.
Common pitfalls
Ignoring abuse reports from blocklists or recipients, allowing spammers to continue unchecked on shared IPs.
Lack of proper segmentation for shared IPs, leading to legitimate senders suffering due to bad actors.
Insufficient monitoring of outbound email traffic for suspicious patterns, allowing spam campaigns to run undetected.
Failing to educate tenants on the importance of maintaining clean mailing lists and proper email hygiene.
Expert tips
Regularly review your hosting provider's reputation management practices before committing to a multi-tenant environment.
If using shared IPs, ensure your email authentication (SPF, DKIM, DMARC) is impeccable to protect your domain's reputation.
Consider investing in a dedicated IP address if your email volume is significant or deliverability is business-critical.
Be proactive in cleaning your email lists and obtaining explicit consent from all recipients to avoid spam complaints.
Marketer view
Marketer from Email Geeks says that understanding the context around multi-tenant hosting IP addresses getting listed on SBL, as opposed to email server/sending IPs, is key.
2019-03-21 - Email Geeks
Expert view
Expert from Email Geeks says that Spamhaus SBL criteria is quite broad. If you're on multi-tenant, it's possible it looks to Spamhaus like it's supporting snowshoers, though that's just a guess without specific listing information.
2019-03-21 - Email Geeks
Safeguarding your email deliverability
Multi-tenant hosting IPs face a heightened risk of being listed on blocklists like the Spamhaus SBL due to the shared reputation model. The actions of a single bad actor can negatively impact the email deliverability of many legitimate senders.
For hosting providers, robust monitoring, strict abuse policies, and strategic IP segmentation are key to mitigating these risks. For tenants, maintaining clean email lists, implementing strong email authentication, and proactively monitoring your sender reputation are essential steps to protect your deliverability.
Ultimately, avoiding SBL listings on shared IPs boils down to a commitment to good email sending practices and a proactive approach to reputation management from all parties involved. If a listing occurs, swift identification of the problem and adherence to de-listing procedures are critical for restoring your email's path to the inbox.
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