What is the recommended soft bounce suppression logic for email?
Michael Ko
Co-founder & CEO, Suped
Published 15 Apr 2025
Updated 19 Aug 2025
7 min read
Managing email bounces is a critical part of maintaining healthy email deliverability and a strong sender reputation. While hard bounces indicate permanent delivery failures and warrant immediate removal from your lists, soft bounces are a bit more nuanced. They represent temporary issues, such as a full inbox or a recipient server being temporarily unavailable. The challenge lies in determining the precise moment when a temporary soft bounce warrants a permanent suppression. It's not always a straightforward decision, and getting it right is key to optimizing your email program.
An overly aggressive soft bounce suppression logic can prematurely remove valid subscribers, leading to lost engagement and revenue opportunities. Conversely, a lenient approach can harm your sender reputation by continuously attempting to send to problematic addresses. This can lead to increased complaints, lower inbox placement rates, and potentially even getting your IP or domain placed on a blocklist (or blacklist).
The goal is to find a balanced soft bounce suppression logic that safeguards your deliverability while maximizing your reach. This involves understanding the different types of soft bounces, setting appropriate thresholds, and continuously monitoring performance. Let's delve into the recommended strategies to help you navigate this complex aspect of email marketing.
Identifying soft bounce types and their significance
Before diving into suppression rules, it's essential to grasp the various types of soft bounces and their implications. Unlike hard bounces, which signify an invalid or non-existent email address, soft bounces suggest a temporary obstacle. Common reasons for a soft bounce include a recipient's mailbox being full, the receiving server being temporarily down, the message size being too large, or even a server throttling incoming mail.
Each soft bounce, even if temporary, contributes to your overall bounce rate. A consistently high soft bounce rate signals to Internet Service Providers (ISPs) that your list might not be well-maintained or that you're sending to disengaged recipients. This can negatively affect your sender reputation, pushing future emails to spam folders or even leading to blacklisting. Understanding the difference between hard and soft email bounces is the first step in effective management.
Moreover, how your email service provider (ESP) handles bounce codes can significantly impact your strategy. While some ESPs automatically retry soft bounces for a set period, it's ultimately your responsibility to implement a robust suppression policy. Neglecting soft bounces can perpetuate poor sending habits and hinder your ability to reach engaged subscribers.
Developing your suppression criteria
The core of soft bounce suppression lies in establishing a clear threshold: how many consecutive soft bounces over what period of time before an address is suppressed? There isn't a universally agreed-upon magic number, as it can depend on your sending volume, frequency, and audience engagement. However, industry guidelines and common practices provide a solid starting point.
Many experts suggest a threshold of three to five consecutive soft bounces within a defined timeframe, typically two weeks to 90 days. This timeframe allows for temporary issues to resolve while preventing excessive attempts to an unresponsive address. For example, the Messaging, Malware and Mobile Anti-Abuse Working Group (M3AAWG) recommends at least two bounces over two weeks. Setting a reasonable soft bounce tolerance is a balance of patience and pragmatism.
Ultimately, the best practice for determining how many soft bounces before suppressing a user involves considering your specific sending patterns and the nature of your email content. Transactional emails, for instance, might warrant a more lenient retry policy than marketing newsletters due to their immediate importance. Here's a table illustrating typical soft bounce scenarios and recommended actions:
Bounce Scenario
SMTP Code (Example)
Recommended Action
Mailbox Full
452 4.2.2
Retry for 72 hours, suppress after 3-5 consecutive bounces within a 30-day window. Consider a re-engagement email after suppression.
Server Unavailable/Busy
450 4.2.0
Retry for 24-48 hours, suppress if consistent after multiple campaigns. May indicate temporary network issues.
Message Too Large
552 5.3.4
Suppress immediately; this is typically a hard bounce reason though classified as soft. Reduce email size and resend if critical.
Greylisting/Temporary Rejection
421 4.7.1
ESPs often handle retries automatically. Monitor for persistent issues. Suppress after 3-5 consistent rejections.
Practical implementation of soft bounce suppression
Once you've defined your soft bounce threshold, the next step is to implement it effectively. This typically involves leveraging your ESP's bounce management features. Most platforms offer configurable settings to automatically suppress email addresses after a certain number of soft bounces. It's crucial to ensure your system distinguishes between different types of temporary delivery failures. For instance, a soft bounce due to a full mailbox might be handled differently than one rejected as spam (even if temporarily).
Automated suppression is vital for efficiency, but there might be cases where manual review is beneficial, especially for high-value contacts or when investigating unusual bounce spikes. Regularly reviewing your suppressed list can also reveal underlying issues, such as outdated data collection practices or a sudden shift in recipient server policies.
A key consideration is whether to temporarily or permanently suppress soft bounces. For most marketing emails, a permanent suppression after hitting your defined threshold is advisable to protect your sender reputation. For transactional emails, you might consider a longer temporary suppression period before permanent removal. If you suppress soft bounces, consider a re-engagement campaign for those contacts before adding them back to your active list.
Best practice: Segmented suppression
Do not treat all soft bounces equally. Distinguish between different bounce codes (e.g., mailbox full vs. transient server error) and apply varying suppression logic. Some temporary errors might resolve quicker or have less impact on your reputation than others. This granular approach allows for more precise list management and better deliverability.
Ongoing management and adaptation
Soft bounce suppression is not a set-it-and-forget-it task. Your email program is dynamic, and so should be your bounce management strategy. Regularly monitor your soft bounce rates, analyze trends, and adapt your suppression logic as needed. Factors such as changes in your sending frequency, new list acquisition methods, or updates in recipient server policies can all influence your soft bounce performance.
Pay close attention to bounce reports provided by your ESP. Look for patterns related to specific domains, content types, or sending times. If you notice an unusually high soft bounce rate from a particular ISP, it might indicate a specific deliverability challenge with that provider that requires a more targeted investigation. Regularly cleaning your list and focusing on engagement can proactively reduce soft bounces and improve overall email deliverability rates.
Common pitfalls
Ignoring SMTP codes: Treating all soft bounces identically, regardless of the specific bounce code or reason provided.
Overly lenient thresholds: Continuing to retry an address too many times, risking sender reputation damage and blocklisting.
Static policies: Not adapting suppression rules to changes in sending behavior or recipient behavior.
Recommended practices
Code-specific handling: Implement logic that varies based on the SMTP bounce code, treating different issues appropriately.
Balanced thresholds: Aim for 3-5 consecutive bounces over 2-4 weeks, or similar rules that prioritize deliverability.
Continuous monitoring: Regularly review bounce reports and adjust your strategy based on performance data.
Views from the trenches
Best practices
Implement a tiered suppression system that escalates actions based on bounce frequency and type.
Actively monitor your bounce rates and analyze the specific SMTP codes for deeper insights.
Regularly clean your email lists by removing consistently problematic addresses, not just those that hard bounce.
Prioritize email authentication protocols like SPF, DKIM, and DMARC to build strong sender reputation.
Segment your audience and tailor sending frequency to reduce engagement-related soft bounces.
Common pitfalls
Ignoring soft bounces, assuming they are always temporary and will resolve themselves without intervention.
Applying a generic, one-size-fits-all suppression rule across all email campaigns and recipient domains.
Not distinguishing between different types of soft bounce reasons, such as full mailboxes versus spam rejections.
Failing to re-engage or re-verify contacts after a period of soft bounces before attempting to resend.
Over-segmenting suppression rules, leading to overly complex and unmanageable email lists.
Expert tips
Analyze historical bounce data to identify patterns unique to your sending practices and audience.
Consider a re-engagement campaign for users who have soft bounced multiple times.
Define clear internal definitions for bounce types to ensure consistent handling across your team.
Be cautious with aggressive suppression, as it might remove valid but temporarily unavailable addresses.
Leverage postmaster tools for domain-specific insights into bounce reasons and reputation.
Expert view
Expert from Email Geeks says that typically three bounces over at least two weeks has been a common guideline for soft bounce suppression.
2023-11-06 - Email Geeks
Expert view
Expert from Email Geeks says that the M3AAWG suggests at least two bounces over at least two weeks on page 11-12 of their Senders BCP.
2023-11-06 - Email Geeks
A balanced approach to email health
Implementing a thoughtful soft bounce suppression logic is a foundational element of effective email deliverability. It's about finding the right balance between patience and pragmatism, ensuring you give legitimate temporary issues time to resolve while swiftly acting to protect your sender reputation from persistent problems. The recommended approach is to define clear thresholds, typically based on a number of consecutive bounces over a set timeframe, and to differentiate actions based on specific bounce codes.
Ultimately, your soft bounce management strategy should be dynamic and informed by ongoing monitoring and analysis of your email performance. By proactively managing soft bounces, you contribute to a cleaner email list, improved inbox placement, and a stronger, more reliable email program overall. Remember that a healthy email list is your most valuable asset in email marketing.
