Why are emails suppressed by an ESP after a subscriber marks them as spam and re-subscribes?
Michael Ko
Co-founder & CEO, Suped
Published 2 Aug 2025
Updated 19 Aug 2025
6 min read
It can be frustrating when a subscriber expresses interest in rejoining your email list after previously marking your emails as spam, only to find they still aren't receiving your messages. You might confirm their re-subscription on your end and see no bounce reports, leaving you wondering why your emails are seemingly disappearing. This situation highlights a complex aspect of email deliverability, deeply rooted in how Email Service Providers (ESPs) and mailbox providers handle spam complaints.
The core of the issue often lies with the ESP's suppression mechanisms, designed to protect your sender reputation and ensure compliance. While it seems counterintuitive that a re-subscribed user wouldn't receive emails, there are critical reasons why an ESP might maintain a suppression even after a user attempts to opt back in.
The impact of a spam complaint
When a subscriber marks an email as spam (often by clicking a 'This is Spam' or 'Report Spam' button in their inbox), this action triggers what's known as a spam complaint. Mailbox providers like Gmail and Yahoo send these complaints back to your ESP via a feedback loop (FBL). This system is designed to provide senders with critical information about how their emails are being received by recipients.
Upon receiving a spam complaint, your ESP takes immediate action to protect your sender reputation and the deliverability of all their clients. The most common response is to automatically add that email address to an internal suppression list, ensuring no further emails are sent to that address. This proactive measure prevents future spam complaints from the same recipient, which would otherwise negatively impact your overall email sending reputation.
Spam complaints and deliverability
A single spam complaint signals to your ESP that a recipient views your messages as unsolicited or irrelevant. Repeated complaints, even from a small percentage of your audience, can significantly damage your domain reputation. This can lead to your emails being directed to the spam folder or even blocklisted by mailbox providers like Gmail and Outlook. It's a defensive posture by ESPs to maintain healthy sending practices for all their users.
ESP suppression mechanisms
Many ESPs implement stringent rules regarding re-subscription after a spam complaint. If a subscriber previously marked your emails as spam, the ESP's internal system often permanently flags that address. This means that even if the subscriber later attempts to re-subscribe, your ESP may not allow it or will continue to suppress emails to that address, regardless of multiple re-opt-in attempts.
This policy protects the ESP from clients who might try to re-add addresses that have previously complained, either intentionally or due to a misunderstanding of email marketing best practices. It's a layer of defense for the ESP's overall sending infrastructure and reputation. An ESP acts defensively to prevent both bad players and naive players from damaging their shared IP pools and domain reputation.
Subscriber's perspective
Desire to rejoin: The user genuinely wants to receive emails again and takes action to re-subscribe.
Expectation of delivery: They assume re-subscription overrides previous actions, leading to confusion when emails don't arrive.
No visible errors: The user checks their spam folder and sees no emails, nor do they receive bounce notifications.
ESP's perspective
Reputation protection: Prioritizes preventing future spam complaints to maintain a healthy sending reputation for all clients.
Immutable suppression: Once an address is flagged due to a complaint, it often remains suppressed, regardless of re-subscription attempts.
Compliance: Adheres to best practices and legal requirements to respect user preferences and avoid unwanted mail.
The silent drop phenomenon
Another complicating factor is the phenomenon of silently dropped emails. In this scenario, your ESP successfully sends the email, and the recipient's mailbox provider (like AOL, Gmail, or Microsoft) accepts it without generating a bounce code. However, the email never actually reaches the subscriber's inbox, not even their spam folder. This can be particularly confusing because there's no clear indication of failure from your side.
Silent drops often occur after a user has marked a previous email as spam. Even if your ESP doesn't explicitly suppress the address internally, the recipient's mailbox provider might still treat future emails from your domain with extreme suspicion. They might accept the email to avoid generating a bounce that could be used for list validation, but then simply discard it without delivering it to the user's mailbox.
When you encounter a situation like this, where a user reports not receiving emails despite re-subscribing and no bounce codes are visible, your ESP's internal suppression list is the first place to investigate. This type of suppression is usually managed on the ESP's side and won't necessarily result in an external bounce code back to your system, as the ESP simply opts not to send the email in the first place.
Understanding suppressed emails without bounce codes
No bounce codes means the ESP is likely suppressing, not the recipient mailbox provider. Check your ESP's internal logs and suppression lists.
Overcoming suppression and best practices
Given these complexities, what can you do if a legitimate subscriber wants to receive your emails again after a spam complaint? The most direct approach is to contact your ESP's support team. They have access to their internal suppression lists and can investigate why a specific address is being suppressed. In some cases, they might be able to manually override the suppression, especially if the subscriber can provide explicit confirmation of their renewed consent.
However, the best long-term strategy is to prevent spam complaints in the first place. Implement a robust opt-in process, ideally double opt-in, to ensure all subscribers genuinely want your emails. This helps reduce the likelihood of a spam complaint and keeps your suppression lists clean. You should also make it very easy for users to unsubscribe, as a clear unsubscribe option can prevent a user from resorting to the 'report spam' button.
Focusing on delivering highly relevant and engaging content to your subscribers is also crucial. When subscribers consistently find value in your emails, they are far less likely to mark them as spam, thereby safeguarding your sender reputation and ensuring your messages reach the inbox. Regularly monitoring your engagement metrics and cleaning your list of inactive subscribers can further enhance your deliverability.
Subscriber must re-subscribe themselves, preferably through a confirmed opt-in process.
Views from the trenches
Best practices
Always use a confirmed double opt-in process to ensure subscribers genuinely want your emails.
Segment your lists and tailor content to ensure high relevance and engagement, reducing complaints.
Regularly clean your email list to remove inactive subscribers and potential spam traps.
Provide a clear, easy-to-find unsubscribe link in every email to prevent spam complaints.
Common pitfalls
Attempting to manually re-add subscribers who have previously complained or unsubscribed without explicit re-consent.
Ignoring spam complaint rates, as they are a critical indicator of list health and sender reputation.
Not integrating feedback loops (FBLs) from major mailbox providers with your ESP's suppression system.
Failing to communicate with your ESP's support when you encounter persistent suppression issues.
Expert tips
Monitor your engagement metrics closely; declining open rates or increasing complaint rates signal issues.
Educate your team on email list management best practices to avoid unintentional re-subscriptions.
Leverage your ESP's analytics and deliverability tools to identify and address suppression causes quickly.
Consider re-engagement campaigns for inactive subscribers before sending them to the suppression list.
Expert view
Expert from Email Geeks says if a subscriber hit the 'This is Spam' (TiS) button, it sends a spam complaint, which would almost certainly cause the Email Service Provider to suppress that address.
2019-10-23 - Email Geeks
Expert view
Expert from Email Geeks says that sometimes a phenomenon called 'silently dropped email' occurs, particularly with Gmail and Microsoft. It's reasonable to assume that after a spam complaint, emails might be dropped silently.
2019-10-23 - Email Geeks
Ensuring email deliverability after a spam complaint
The suppression of emails by an ESP after a subscriber marks them as spam, even upon re-subscription, is a crucial aspect of email deliverability designed to protect sender reputation and maintain compliance. While it can be frustrating for marketers and subscribers alike, these measures are in place to ensure a healthy email ecosystem. Understanding the underlying reasons, such as internal suppression lists and silent drops, is key to navigating these challenges.
Prioritizing strong consent mechanisms, providing clear unsubscribe options, and delivering valuable content are the most effective ways to minimize spam complaints and avoid future suppression issues. By adhering to these best practices and working closely with your ESP, you can ensure your legitimate emails reach the intended inboxes.
Microsoft) accepts it without generating a bounce code. However, the email never actually reaches the subscriber's inbox, not even their spam folder. This can be particularly confusing because there's no clear indication of failure from your side.
