Summary
Many email marketers seek precise documentation detailing different bounce types and definitive thresholds for when to suppress email addresses. While a single, universally accepted document with specific rules (like "suppress after 3 hard bounces") does not exist, the general consensus across the industry and various platforms points to a nuanced approach to bounce management. Understanding the distinction between hard and soft bounces, and the underlying reasons (SMTP codes), is crucial for maintaining sender reputation and ensuring optimal deliverability.
Key findings
- No universal standard: There is no single, industry-wide document that dictates exact numerical thresholds for suppressing email addresses based on bounce types.
- ESP-specific rules: Most Email Service Providers (ESPs) implement their own internal bounce classification and automated suppression logic.
- Hard vs. soft bounces: Hard bounces generally signify permanent delivery failures (e.g., invalid address), while soft bounces indicate temporary issues (e.g., mailbox full). More details can be found in our guide on the difference between hard and soft email bounces.
- Sender reputation impact: Failing to address bounces, particularly hard bounces, can severely damage your sender reputation and lead to poor inbox placement.
- Focus on root cause: Understanding the specific reason for a bounce (often indicated by an SMTP bounce code) is more important than simply counting bounces, as some soft bounces are recoverable.
Key considerations
- Automated suppression: Most ESPs automatically place hard-bouncing addresses on a suppression list to protect your sending reputation.
- Soft bounce strategy: Soft bounces may be retried, but persistent soft bounces (e.g., multiple "mailbox full" errors) should eventually lead to suppression to avoid future deliverability issues. Mailchimp provides a good overview of their bounce handling.
- List hygiene: Regular cleaning of your email lists is paramount to minimizing overall bounce rates and maintaining a healthy sender reputation.
- Continuous monitoring: Actively monitor your bounce rates and DMARC reports to identify trends and address potential issues proactively.
What email marketers say
Email marketers often express a desire for concrete, numerical guidelines on when to suppress email addresses based on bounce types. They frequently rely on the bounce handling policies of their specific Email Service Providers (ESPs) and share anecdotal experiences regarding what constitutes an acceptable bounce threshold, whether it's for hard bounces or various forms of soft bounces like a full mailbox.
Key opinions
- Desire for simplicity: Many marketers prefer straightforward rules, such as suppressing after a set number of soft bounces, to simplify bounce management.
- ESP reliance: Most marketers trust their ESP's built-in bounce handling, including automated suppression for hard bounces and retries for soft bounces.
- Historical guidelines: Some recall older, more prescriptive documents, perhaps from legacy services like Return Path, that offered specific bounce thresholds.
- Understanding specifics: Marketers are keen to understand if specific bounce codes (e.g., 5.2.1 reputation-based bounces) require different handling. Our article on processing 5.2.1 reputation-based bounces delves deeper.
- Impact on campaigns: The underlying goal is to prevent bounces from negatively affecting campaign performance and sender reputation.
Key considerations
- Trusting ESP logic: For many, the default bounce handling of their ESP (e.g., Klaviyo's bounce management, as Klaviyo explains) is sufficient for most scenarios.
- Manual overrides: Some marketers may consider manual suppression for consistently soft-bouncing addresses, particularly those marked as "mailbox full" after multiple attempts.
- List validation: Pre-sending list validation is often highlighted as a key practice to reduce initial hard bounce rates significantly. Learn more about managing hard bounced email addresses.
- Monitoring bounce categories: Paying attention to categories like "disabled mailbox" bounces is important for effective list segmentation and clean-up.
Marketer view
Marketer from Email Geeks recalls seeing an older document that detailed specific bounce types and the number of bounces after which an email address should be suppressed.
Marketer view
Marketer from Email Geeks confirms they also remember seeing such a document, specifically mentioning a chart or guide from a previous employer.
What the experts say
Deliverability experts advocate for a strategic approach to bounce handling that goes beyond simple counts. They emphasize the importance of understanding the nuances of SMTP response codes and the long-term impact on sender reputation. While automated systems handle many bounces, experts stress the need for marketers to gain deeper insights into why emails are bouncing to implement more effective list management and sending practices.
Key opinions
- Contextual understanding: Experts advise focusing on the specific type of bounce (hard vs. soft) and the underlying SMTP error code to determine the appropriate suppression action, rather than relying on generic numerical rules.
- Aggressive hard bounce suppression: Permanent bounces (hard bounces) should be suppressed immediately to protect sender reputation. Our guide on acceptable email bounce rates provides further context.
- Careful soft bounce management: Soft bounces may warrant retries, but persistent soft bounces (e.g., repeated "mailbox full") should eventually lead to suppression to prevent reputation degradation. Refer to recommended soft bounce suppression logic.
- Proactive hygiene: Preventing bounces through robust list acquisition practices and regular cleaning is more effective than reactive suppression.
- Beyond the numbers: Simple numerical rules (like "3 hard bounces") often oversimplify the complex dynamics of email delivery and can be misleading without proper context.
Key considerations
- Monitor SMTP codes: A deep understanding of SMTP response codes (e.g., 4xx for temporary, 5xx for permanent failures) is essential for accurate bounce classification and handling.
- Avoid excessive retries: Continuously sending to soft-bouncing addresses can negatively impact your sender reputation, even if they aren't hard bounces.
- Engagement segmentation: Suppressing unengaged subscribers can indirectly reduce soft bounces from inactive or neglected mailboxes, improving overall list health.
- Leverage DMARC reports: DMARC reports provide aggregated bounce data that can help identify persistent issues or unexpected bounce types. Mailgun offers insights on what to do about them.
Expert view
Expert from Spam Resource highlights that simplistic rules like "3 hard bounces then suppress" don't account for the complexity of different bounce types and the specific reasons behind them.
Expert view
Expert from Word to the Wise advises that permanent failures (5xx SMTP codes) should lead to immediate suppression, as retrying these addresses is futile and harmful to reputation.
What the documentation says
Official documentation from various Email Service Providers and industry bodies consistently defines bounce types based on their permanence and outlines the general principles for managing them. While specific numerical thresholds for suppression are rare, the documentation invariably emphasizes the importance of promptly handling hard bounces and carefully managing persistent soft bounces to protect sender reputation and ensure email deliverability. These resources often refer to SMTP response codes as the fundamental indicators for bounce classification.
Key findings
- Standard classifications: Documentation typically categorizes bounces into 'hard' (permanent failure) and 'soft' (temporary failure) based on RFC-defined SMTP error codes.
- Automated handling: Most ESPs describe automated processes for handling hard bounces, immediately adding them to a suppression list. AWS discusses dealing with bounced emails in this context.
- Soft bounce retries: Soft bounces are usually retried over a period, but if persistent, they are often converted to hard bounces or suppressed. See our guide on definitions and utility of block, soft, and hard bounces.
- Reputation impact: Documentation consistently warns that high bounce rates, especially hard bounces, negatively affect sender reputation and can lead to IP or domain blocklisting.
- Detailed bounce data: Many platforms provide detailed bounce reports, including specific error messages and SMTP codes, to aid in diagnosis.
Key considerations
- Adherence to ISP policies: Providers like Higher Logic recommend manually suppressing certain contacts or setting a hard bounce suppression threshold for the account based on their policies. (Higher Logic's Bounce Types).
- Understanding RFCs: The technical foundation for bounce handling lies in SMTP bounce codes and their classifications as defined in RFCs, which provide a universal language for email delivery issues.
- Configurable settings: Some documentation highlights options for customizing soft bounce retry logic or setting specific suppression rules within the platform.
- Proactive list management: Emphasis is consistently placed on acquiring clean lists and regular maintenance to prevent bounces rather than just reacting to them.
Technical article
Documentation from Klaviyo Help Center states that a "bounce" occurs when an email cannot be delivered and categorizes these into soft and hard bounces, explaining the typical reasons for each.
Technical article
Documentation from Amazon Web Services, Inc. (AWS) advises users on how to handle bounced emails within SES, including automatically adding certain bounced emails to the suppressed list.
Related resources
7 resources
Related pages
What is the difference between hard and soft email bounces and how should they be managed?
Should you resend emails to hard bounces, and how are hard and soft bounces defined?
How should 4xx mail errors be handled and when should they be considered bounces?
How do email service providers manage soft and hard bounces, bounce codes, and soft bounce tolerance?
What are the definitions and utility of block, soft, and hard email bounces?
How to manage hard bounced email addresses for future sends?
Which SMTP bounce codes should lead to mailing list suppression?
What is the recommended soft bounce suppression logic for email?
How do email service providers classify and manage SMTP bounce codes for deliverability?
What is an acceptable email bounce rate, and how do hard and soft bounces differ?
