Should ESPs use global suppression lists for hard bounces across different customers?
Matthew Whittaker
Co-founder & CTO, Suped
Published 8 May 2025
Updated 16 Aug 2025
8 min read
The question of whether email service providers (ESPs) should use global suppression lists for hard bounces across different customers is a nuanced one. On the surface, it might seem like a straightforward way to maintain a clean sending environment and protect the reputation of shared IPs.
Hard bounces indicate a permanent delivery failure, meaning the email address simply doesn't exist or is otherwise invalid. Continuing to send to such addresses can severely harm a sender's reputation, leading to lower inbox placement rates and even blocklisting. So, if an ESP knows an address is bad for one customer, why send to it for another?
However, the practice isn't as simple as it appears, bringing into play considerations around data privacy, legal compliance (like GDPR), and the potential for unintended consequences. Let's delve into the various facets of this discussion.
Understanding global suppression lists
A suppression list is a collection of email addresses that an ESP will not send messages to, regardless of a customer's mailing list. These lists are crucial for maintaining good email deliverability. They typically include addresses that have unsubscribed, marked an email as spam, or resulted in hard bounces.
When we talk about global suppression lists (GSLs), we're referring to a list maintained by the ESP that applies across all their clients. For instance, Amazon SES Global Suppression List is an example where if any customer sends an email that hard bounces, that address is added to a list that prevents all SES customers from sending to it. This approach is rooted in the idea of collective reputation management, particularly for shared IP pools.
The primary benefit of a global hard bounce list is the immediate prevention of sending to known invalid addresses, which helps protect the ESP's overall sending infrastructure and, by extension, all customers using that infrastructure. This preventative measure can reduce hard bounce rates across the board, which is a significant factor in maintaining a healthy sender reputation and avoiding a widespread email blocklist (or blacklist) for the ESP.
Best practice: hard bounce management
Regardless of whether an ESP uses a global suppression list, individual senders must actively manage hard bounced email addresses. Prompt removal of these addresses is critical for maintaining strong sender reputation. Explore how to manage hard bounced email addresses for future sends to ensure optimal email deliverability.
Global versus customer-specific suppression
The core of the debate lies in whether hard bounce data from one customer's sends should inform suppression for another, unrelated customer. From a technical standpoint, preventing sends to non-existent addresses is always beneficial for deliverability across shared IP pools. However, legal and ethical concerns arise when an ESP aggregates and utilizes data across different client bases.
One perspective argues that an email address that hard bounces is simply non-existent. It’s an absence of data, not personally identifiable information (PII). If the global list only contains the email address itself, without any associated personal data about the individual, then its use might not constitute a privacy violation. This could allow ESPs to keep their sending infrastructure cleaner, benefiting all users by reducing overall bounce rates and improving shared IP reputation.
Conversely, even a non-existent email address can be linked to an individual if it once belonged to them, or if it is part of a list that includes other PII managed by the ESP's clients. The GDPR and ESP Suppression Lists highlights the complexities. If an ESP uses such a global list, they risk moving from a 'data processor' role (simply handling data on behalf of clients) to a 'data controller' role (determining the purposes and means of processing personal data), which carries significantly higher legal responsibilities.
This shift in legal responsibility is a major deterrent for many ESPs. The ownership of an invalid or shut-down email address is debatable. If a user previously held that address and it was associated with their personal activities, they might still consider it their data, even if it's no longer active. This makes broad, cross-customer sharing of hard bounce data a risky proposition from a privacy perspective.
Global suppression (across customers)
Reputation management: Proactively protects shared IP addresses from known bad email addresses.
Efficiency: Reduces overall hard bounce rates for the entire ESP platform.
Compliance risk: High risk of becoming a data controller under privacy regulations.
Data accuracy: Potential for false positives if a hard bounce was temporary or erroneous.
Customer-specific suppression
Data privacy: ESP remains a data processor, respecting client data ownership.
Client control: Clients manage their own suppression lists based on their specific bounce data.
Reputation impact: Individual customer's poor list hygiene can impact shared IP reputation.
Scalability: Less effective at preventing large-scale hard bounces across diverse customer bases.
Technical and compliance considerations
The distinction between an ESP acting as a data processor and a data controller is crucial for compliance. As a data processor, an ESP processes data solely on behalf of their clients, who are the data controllers. If an ESP independently decides to use hard bounce data from one client to prevent another client from sending to that address, they are making a decision about the processing of that data, which could elevate them to a data controller role. This carries significant legal ramifications, particularly under regulations like GDPR or CCPA.
Another consideration is the occurrence of false positives in hard bounces. While less common than soft bounces, an email reported as a hard bounce might occasionally be a temporary issue or an error. If an address is globally suppressed based on a false positive, it could prevent a legitimate sender (another customer of the ESP) from reaching a valid subscriber. This could lead to customer frustration and complaints.
Some ESPs might employ a global blocklist (or blacklist) for hard bounces under specific circumstances, such as when a domain consistently generates hard bounces for multiple unrelated clients, indicating a systemic issue rather than just individual bad addresses. However, this is typically done with extreme caution and clear policies to mitigate legal and reputational risks. Understanding how different bounce types are handled by ESPs is key.
Impact on deliverability and reputation
From a deliverability perspective, minimizing hard bounces is paramount. Hard bounces significantly damage sender reputation. If an ESP's IPs are frequently hitting invalid addresses, they are more likely to be blocklisted (or blacklisted) by mailbox providers. This affects every customer sending through those IPs.
While a global hard bounce suppression list could theoretically reduce overall hard bounce rates for the ESP, its practical effectiveness may be limited, as some ESPs have found. Individual customer list hygiene remains the most impactful factor. If individual customers are sending to very old or poorly acquired lists, a global hard bounce list might only catch a fraction of the problematic addresses. This is why sharing bounce data with clients is so vital.
Ultimately, the decision to implement a global hard bounce list across different customers balances the benefits of collective reputation management against significant data privacy and legal risks. Most ESPs lean towards customer-specific suppression for hard bounces, ensuring clients maintain control over their data and avoiding potential legal complications. They provide tools and guidance for customers to manage their own bounces, which is generally more effective for long-term deliverability success.
Views from the trenches
Best practices
Actively remove all hard bounced email addresses from your lists immediately.
Implement double opt-in to ensure subscribers are genuinely interested and email addresses are valid.
Regularly monitor your bounce rates and investigate any sudden increases.
Segment your audience and send relevant content to reduce unengaging sends.
Ensure proper email authentication records like SPF, DKIM, and DMARC are set up.
Common pitfalls
Failing to promptly remove hard bounces, which harms sender reputation.
Ignoring bounce reports provided by your ESP or email analytics tools.
Purchasing or using old, unverified email lists that contain many invalid addresses.
Not understanding the difference between hard and soft bounces and how to handle them.
Over-reliance on an ESP's global list instead of managing your own list hygiene.
Expert tips
Focus on robust list hygiene practices at the client level.
Educate clients on the importance of managing their hard bounces.
Understand the legal implications of data processing across different clients.
Prioritize preventing bounces at the source through good list acquisition.
Use email validation services before sending to new or aged lists.
Expert view
Expert from Email Geeks says that ESPs generally let each user or list manage their own hard bounces without sharing across unrelated customers.
2021-06-09 - Email Geeks
Marketer view
Marketer from Email Geeks says that comingling data for a global suppression list across different ESP customers would not make sense from a customer perspective.
2021-06-09 - Email Geeks
Striking the balance
The question of whether ESPs should use global suppression lists for hard bounces across different customers is complex. While such a practice could offer some technical benefits for shared IP reputation, the significant legal and data privacy risks associated with it typically outweigh these advantages.
Most reputable ESPs prioritize respecting their role as data processors and empower their clients with the tools and data necessary to manage their own suppression lists effectively. This approach ensures greater compliance and allows clients to maintain ownership and control over their subscriber data, including managing various bounce types that can impact deliverability.
For email marketers, the takeaway is clear: robust list hygiene and prompt hard bounce management at the individual client level are always the best practices. This proactive approach contributes far more to sustained deliverability and a strong sender reputation than relying solely on a potential global blacklist (or blocklist) for hard bounces.
