Should email spam complaints be suppressed across multiple ESPs?
Matthew Whittaker
Co-founder & CTO, Suped
Published 1 Jun 2025
Updated 18 Aug 2025
7 min read
Many businesses, especially those with diverse email sending needs, find themselves using multiple Email Service Providers (ESPs). One ESP might handle marketing campaigns, while others manage transactional emails such as order confirmations or password resets. This setup can introduce complexities, particularly when it comes to managing spam complaints and ensuring consistent sender reputation across all platforms.
A common question that arises in such multi-ESP environments is whether spam complaints received through one ESP should lead to the suppression of that email address across all other ESPs you use. It is easy to think of each ESP as a silo, where a complaint on one does not necessarily impact the others, but this perspective can be detrimental to your overall email deliverability.
The core of this issue lies in maintaining a strong and consistent sender reputation. Ignoring complaints on one platform while sending to the same recipient via another can signal to Internet Service Providers (ISPs) that your sending practices are inconsistent or, worse, malicious. Let's delve into why a unified approach to spam complaint suppression is generally the best practice, with some nuanced exceptions.
The critical role of suppression lists
Suppressing email addresses that have filed spam complaints is a fundamental aspect of good email deliverability. When a recipient marks your email as spam, it sends a strong signal to their mailbox provider, influencing your sender reputation. If you continue to send emails to this recipient, it can significantly harm your standing with ISPs, leading to lower inbox placement rates and potentially even domain or IP blocklisting (also known as blacklisting).
Email Service Providers (ESPs) and mailbox providers use Feedback Loops (FBLs) to report spam complaints back to senders. These FBLs are crucial mechanisms that allow you to identify recipients who no longer wish to receive your emails. Upon receiving an FBL report, it is standard practice for your ESP to immediately add the complained-about address to a suppression list to prevent future sends to that user.Feedback loops are key for maintaining a clean list.
The immediate impact of a spam complaint
When a subscriber marks an email as spam, your ESP (or the sending platform) typically records this event and automatically prevents further sends to that specific email address from that particular ESP. This is an essential first step in preventing repeated complaints, which can severely impact your sender reputation. Mailbox providers like Gmail and Outlook are highly sensitive to user feedback, and complaints are a strong negative signal.
While immediate suppression by a single ESP is vital, the true challenge arises when you operate across multiple platforms. Each ESP might manage its own suppression list, meaning a complaint registered on ESP A doesn't automatically prevent you from sending to that same recipient via ESP B.
Navigating multiple ESPs and sender reputation
Operating with fragmented suppression lists can lead to significant problems. Even if each individual ESP is diligent in suppressing complaints on its end, the overall perception from mailbox providers is that of your sending domain or IP. If they see continued mail from your brand reaching a recipient who has already complained, it sends a mixed message about your commitment to good sending practices. This can contribute to a damaged email domain reputation, regardless of which ESP sent the problematic email.
Inconsistent suppression also increases the risk of being added to blocklists (or blacklists). Most blocklists operate by observing sending behavior across the internet. If an email address reports your marketing emails as spam, and you then continue to send to that address from a different ESP, it can increase your overall spam complaint rate, making you more susceptible to being listed. You can learn more about email blocklists and how they work.
Problem: siloed suppression
Inconsistent data: Each ESP holds its own complaint data, leading to a fragmented view.
Repeated complaints: Addresses suppressed on one ESP might still receive mail from another.
Reputation fragmentation: Mailbox providers may see conflicting signals from your brand.
Increased blocklist risk: Higher overall complaint rates increase the chances of being blocklisted.
Solution: centralized suppression
Unified complaint data: All complaints feed into a single, master suppression list.
Improved reputation: Demonstrates consistent and responsible sending across all channels.
Better deliverability: Higher chance of reaching the inbox for legitimate emails.
While the general rule is to suppress across the board, it's essential to differentiate between marketing and truly transactional emails. The impact of a spam complaint on a marketing email is typically different from one on a transactional email.
Differentiating transactional from marketing complaints
Transactional emails are typically defined as emails that facilitate an agreed-upon commercial transaction or update. Examples include password resets, purchase receipts, shipping notifications, and two-factor authentication codes. These emails are critical for user experience and platform functionality. If a user accidentally marks a transactional email as spam, suppressing them from receiving future crucial communications can lock them out of your service or prevent them from accessing vital information.
Marketing emails, on the other hand, are promotional in nature and are sent with the primary goal of engaging or selling to a user. A spam complaint on a marketing email is a clear indication that the recipient no longer wants to receive promotional content. Failing to suppress these complaints across all ESPs means you might continue to annoy the user, leading to more complaints, decreased engagement metrics, and a higher risk of being seen as a spammer by ISPs. Industry standard for spam complaints is less than 0.02%.
Example of a suppressed email address
email@example.com
Given this distinction, a nuanced strategy is often best. While you should almost always suppress marketing email complaints across all ESPs, you might consider an exception for essential transactional emails. However, this exception should be carefully managed to avoid unintended negative consequences. You can read more about why emails are suppressed after a spam complaint, even if a user re-subscribes.
Implementing a unified suppression strategy
To effectively manage spam complaints across multiple ESPs, proactive strategies are necessary. This involves creating a centralized, master suppression list that aggregates complaints from all your sending platforms. This list should be regularly updated and shared across your ESPs. For example, if you receive a complaint through ESP A, that email address should be added to your master suppression list, which then prohibits sends from ESP B and ESP C for marketing communications.
Regularly monitoring your complaint rates across all sending channels is also critical. Tools like Google Postmaster Tools and other FBL services provide insights into how your mail is performing. If you observe a spike in complaints, it's a signal to review your sending practices, list hygiene, and potentially your consent acquisition methods. Keeping a close eye on these metrics allows you to react quickly and mitigate potential deliverability issues before they escalate into major problems, such as widespread blocklisting.
Aspect
Marketing emails
Transactional emails
Purpose
Promotional, engagement, sales
Facilitate a transaction or core service functionality
Suppression across ESPs
Strongly recommended for all ESPs (e.g., Mailgun, SendGrid)
Consider exceptions for critical communications to prevent user lockout
Less direct impact, but can indicate user frustration or accidental clicks
Best practices for unified suppression
Automate sync: Implement automated processes to export and import suppression lists between your ESPs daily or hourly.
Central database: Maintain a single, definitive master suppression list outside of any single ESP.
Clear categorization: Tag email addresses based on their complaint type (marketing, transactional) if you apply different suppression rules.
Audit regularly: Periodically review your suppression processes and lists for accuracy.
Unified suppression for superior deliverability
While the idea of sharing complaint suppression across all ESPs seems like a straightforward best practice, the distinction between marketing and transactional emails adds a layer of complexity. For marketing emails, universal suppression is almost always the right choice to protect your sender reputation and ensure you are respecting recipient preferences. However, for genuinely transactional emails, a more nuanced approach may be required to prevent disrupting user access to critical services. The key is to implement robust processes that ensure consistency where it matters most, allowing for exceptions only where strictly necessary and clearly defined.
Views from the trenches
Best practices
Implement a centralized suppression database to manage complaints from all ESPs.
Automate the synchronization of suppression lists across all your email sending platforms.
Regularly monitor overall spam complaint rates, not just per-ESP rates, to track your reputation.
Common pitfalls
Failing to sync suppression lists between ESPs, leading to continued sends to disengaged users.
Treating transactional and marketing email complaints the same, potentially locking out users from essential services.
Not having a clear process for identifying and acting on FBLs from all sending sources.
Expert tips
For marketing emails, a spam complaint should immediately halt sending from all ESPs you use for that recipient.
Carefully define what constitutes a 'transactional' email that might warrant an exception to universal suppression.
Ensure your suppression system prioritizes the recipient's preference above all else to maintain trust and deliverability.
Expert view
Expert from Email Geeks says that failing to suppress complaints across different ESPs for the same business entity, while unwise, is not typically classified as snowshoe spamming behavior, which has a more specific definition.
2023-10-10 - Email Geeks
Expert view
Expert from Email Geeks says that for truly transactional emails like receipts or password resets, suppressing for complaints is generally not recommended as it can prevent users from accessing critical services.
Gmail and 
Outlook are highly sensitive to user feedback, and complaints are a strong negative signal.
(e.g., Mailgun, 
SendGrid)
