Should I use a backup ESP when my primary ESP is blocked by Spamhaus?
Michael Ko
Co-founder & CEO, Suped
Published 16 Apr 2025
Updated 16 Aug 2025
7 min read
When your primary email service provider (ESP) suddenly gets listed on a major blocklist like Spamhaus, it can cause immediate panic. The instinct might be to find a quick fix, such as redirecting all your email traffic to a backup ESP. This approach seems logical on the surface, aiming to restore email flow and maintain business operations without interruption.
However, the reality of email deliverability, sender reputation, and how blocklists function means that simply switching to a secondary provider when your primary is experiencing issues is rarely a sustainable or effective solution. It can often lead to further complications, potentially spreading the problem rather than containing it.
Understanding the underlying reasons for a Spamhaus listing and the intricacies of email infrastructure is vital before making such a critical decision.
Spamhaus is one of the most respected and widely used anti-spam organizations, maintaining various blocklists (or blacklists) to help internet service providers (ISPs) filter out unwanted email. These lists identify IP addresses and domains associated with spamming, malware, and other malicious activities.
A listing on a Spamhaus blocklist means that emails originating from the listed IP or domain are likely to be rejected or heavily filtered by many mail servers worldwide. Common reasons for an ESP's IP or domain to be listed include sending to spam traps, high complaint rates, or unusual sending patterns that resemble spam. In some cases, a re-engagement campaign with an old, uncleaned list can trigger a listing. You can learn more about why your domain or IP might be blocked by Spamhaus and how to resolve it.
While Spamhaus provides various lists, such as the Spamhaus Blocklist (SBL) for known spam sources and the Policy Blocklist (PBL) for IPs that should not be sending direct email, the impact on deliverability is significant across the board. The goal of these lists is to maintain a healthy email ecosystem by preventing bad actors from delivering their messages. The process for getting delisted involves identifying and rectifying the root cause of the listing, which an ESP usually handles in coordination with you.
The challenges of a backup ESP strategy
The idea of a backup ESP might seem like a solid contingency plan, but it presents several significant challenges in the context of email deliverability and reputation.
IP warming and reputation
One of the biggest hurdles is maintaining a sufficient sending volume on the backup ESP to ensure its IPs (and your domain) stay warm and retain a good reputation. Email providers judge sender reputation based on consistent sending volume and positive engagement. If you only send minimal volume through your backup ESP, its IPs will be unwarmed and sudden large increases in volume, such as when your primary ESP is blocked, will immediately flag them as suspicious. This could lead to filtering or even new blocklistings on the backup ESP.
Lack of transparency and control
Many ESPs, particularly those offering dedicated IP addresses, are very sensitive about their sender reputation. If you abruptly switch large volumes of email, especially email that has just caused a blocklist event on another provider, the backup ESP might view this as an attempt to circumvent their rules or evade deliverability issues. This could result in your account being suspended or terminated by the backup provider, leaving you in a worse position. When your IP gets blocklisted, it's crucial to address the problem at its source.
Furthermore, managing DNS records for two ESPs, particularly for advanced configurations like SPF, DKIM, and DMARC, adds significant complexity. Ensuring consistent authentication across both providers, especially during a crisis, is challenging and prone to errors. Improper SPF or DKIM setup can further damage your domain's reputation.
Parallel ESP usage versus backup for blacklists
While a dedicated backup ESP for blacklisting scenarios is generally not advisable, using multiple ESPs for different purposes is a common and often effective strategy. Many organizations use one provider for marketing emails and another for transactional messages, or even separate providers for different regions or brands. This parallel usage allows each ESP to build and maintain a distinct reputation based on the specific type and volume of mail they handle.
The key distinction is that these setups are typically designed for concurrent, specialized sending, not as a rapid failover in case of a blocklist event. If a marketing ESP gets listed, the transactional ESP continues sending critical emails because its sending patterns and IP reputation are separate.
Some organizations also maintain both shared and dedicated IP environments with the same ESP, allowing flexibility. However, these are strategic choices for redundancy and traffic segmentation, not a reactive measure against a Spamhaus listing. The fundamental issue with a blocklist is often the content or list quality, which would simply transfer to the backup ESP.
Focusing on the root cause and prevention
Instead of seeking a backup ESP to circumvent a Spamhaus blocklist, the focus should be on identifying and rectifying the root cause of the listing. This typically involves a thorough audit of your email program, list hygiene practices, and sender authentication.
List hygiene and permission
Spamhaus listings are frequently a symptom of poor list quality or inadequate permission practices. Sending to old, unengaged, or purchased lists significantly increases the risk of hitting spam traps or generating spam complaints. Implementing a confirmed opt-in process and regularly cleaning your lists to remove inactive or problematic subscribers is crucial. A high spam rate often indicates issues with list quality.
Sender authentication and content
Ensuring your email authentication records (SPF, DKIM, DMARC) are correctly configured is fundamental. This helps mailbox providers verify your identity and trust your emails. Additionally, regularly reviewing your email content for spammy triggers and maintaining a good reputation with your current ESP by adhering to best practices are far more effective long-term strategies. When your IP or domain ends up on a blacklist, the best approach is to identify and correct the underlying problem with your sending practices.
Views from the trenches
Best practices
Maintain robust list hygiene: regularly clean your email lists to remove inactive subscribers, bounces, and known spam traps.
Implement confirmed opt-in (double opt-in) for all new subscribers to ensure explicit consent and reduce spam complaints.
Segment your email sending by type (e.g., transactional, marketing) and volume, potentially across different IPs or subdomains.
Ensure all email authentication protocols (SPF, DKIM, DMARC) are correctly configured and monitored for compliance.
Common pitfalls
Attempting to use a secondary ESP as a quick fix for a Spamhaus blocklist without addressing the root cause of the listing.
Failing to warm up new IPs or domains on a backup ESP, leading to poor deliverability or new blocklistings when traffic is diverted.
Switching large volumes of problematic email traffic to a backup ESP, which can result in the backup provider also suspending your account.
Not thoroughly cleaning email lists after a blocklist event, meaning the underlying issue persists regardless of the sending platform.
Expert tips
A Spamhaus listing typically signals deeper issues with your email practices; fixing these is more effective than simply changing providers.
Maintaining a live, warmed infrastructure on multiple platforms, with traffic split, is a more robust disaster recovery strategy than a cold backup.
If you get listed, the fastest path to resolution is usually working with your current ESP and Spamhaus to fix the original issue.
Be prepared for difficult conversations about your data quality if a significant portion of your list is causing blocklistings.
Expert view
Expert from Email Geeks says that clients often ask about backup ESPs, but the main issue is their inability or unwillingness to provide sufficient volume to the backup system to maintain its reputation.
2022-03-09 - Email Geeks
Marketer view
Marketer from Email Geeks says that some clients use multiple SES regions for primary and backup, but a truly separate company for transactional email redundancy proved too complex due to additional processes and requirements.
2022-03-09 - Email Geeks
The path forward: prevention and resolution
While the temptation to switch to a backup ESP when your primary provider is blocked by Spamhaus is understandable, it's generally not a recommended long-term solution. Such a reactive measure often transfers the problem rather than solving it, potentially damaging your reputation with multiple providers. The most effective strategy involves understanding how to deal with being blocklisted by Spamhaus by addressing the root cause, typically related to list quality and sending practices.
Investing in robust list hygiene, implementing confirmed opt-in, and adhering to email sending best practices are the cornerstones of maintaining excellent deliverability and avoiding blocklists. This proactive approach ensures your email program is resilient and trustworthy, regardless of any temporary issues with a specific provider.
Spamhaus
0Spam
Cisco
NoSolicitado
URIBL
abuse.ro
ALPHANET
Anonmails
Ascams
BLOCKEDSERVERS
Calivent Networks
EFnet
JustSpam
Kempt.net
NordSpam
RV-SOFT Technology
Scientific Spam
Spamikaze
SpamRATS
SPFBL
Suomispam
System 5 Hosting
Team Cymru
Validity
www.blocklist.de Fail2Ban-Reporting Service
ZapBL
2stepback.dk
Fayntic Services
ORB UK
technoirc.org
TechTheft
