How long should emails be kept in a bounce email inbox?

Key findings

• Automation is key: Most email platforms process bounces automatically, meaning bounce emails rarely need to sit in a manual inbox. This automation ensures timely removal of problematic addresses.
• Hard bounces: Addresses causing hard bounces (permanent delivery failures) should be removed from your mailing list immediately to protect your sender reputation. Trying to resend to these addresses is detrimental. More information on this can be found in our guide on how to manage hard bounced addresses.
• Soft bounces: For soft bounces (temporary issues), a limited number of retries may be acceptable before the address is suppressed. The common recommendation is to suppress after around 6 consecutive soft bounces.
• Diagnostic retention: If bounce emails are kept at all, it's typically for after-the-fact diagnostics or specific requests from mailbox providers, not for routine processing. A retention period of a week or so for such diagnostic purposes is generally sufficient.

Key considerations

• Sender reputation: Maintaining a low bounce rate (ideally below 2%) is crucial for a healthy sender reputation. High bounce rates can signal poor list hygiene and lead to your emails being flagged as spam or even blacklisted (blocklisted).
• ISP expectations: Many mailbox providers prefer senders to manage bounces by analyzing SMTP transaction logs rather than relying on bounced emails. They expect senders to proactively remove invalid addresses.
• Classification: Understanding the difference between hard and soft bounces is critical for implementing proper bounce management rules.
• Data storage: While the bounce email itself may not need long-term storage, the bounce data (reason, date, recipient) should be logged for analytical purposes, to help improve list hygiene and campaign performance.
• Automated clean-up: Ensure your email service provider (ESP) or internal system automatically cleans hard bounces and implements a clear soft bounce suppression logic.

Key opinions

• Automated processing: Many marketers primarily rely on bounce processing automation, which sends bounces directly to a system for handling, eliminating the need for them to hit a physical inbox.
• Limited diagnostic retention: If bounce emails are kept in an inbox, it's generally for diagnostic purposes after the fact, not for everyday use. This might involve keeping copies for a week or so.
• Hard bounce immediate removal: There's a strong consensus that hard bounced email addresses should be removed from mailing lists immediately and automatically to prevent further deliverability issues.
• Soft bounce tolerance: For soft bounces, a moderate approach is recommended, allowing a certain number of temporary failures (e.g., 6 attempts) before suppressing the address.

Key considerations

• Efficiency: Manual review of bounce inboxes is largely inefficient and outdated, highlighting the need for robust automated systems. You can read more about best practices for managing bounces.
• Deliverability impact: Ignoring bounces or resending to hard bounced addresses can severely damage sender reputation and inbox placement. A healthy bounce rate is typically less than 2%, as advised by SendLayer.
• Understanding bounce types: Differentiating between soft and hard bounces (permanent vs. temporary) is fundamental for effective bounce management strategies, as highlighted by Mailgun.
• List hygiene: Proactive list cleaning and bounce management are essential for maintaining the quality of your email list and ensuring messages reach their intended recipients. Our guide on cleaning up soft bounces explains this further.

Key opinions

• Transaction-time rejections: Most major mailbox providers reject mail at the SMTP transaction time, providing instant feedback via error codes, rather than sending a separate bounce email.
• Log lines over inboxes: Experts prefer analyzing server log lines for bounce reasons, as this data is more immediate and detailed than parsing bounce messages in an inbox.
• Immediate hard bounce removal: Permanent failures (hard bounces) necessitate immediate and permanent removal from the mailing list to prevent harm to sender reputation and avoid hitting spam traps.
• Strategic soft bounce handling: Soft bounces, while temporary, should still be managed with a defined retry policy and eventual suppression to prevent persistent, unresolvable issues from affecting deliverability.

Key considerations

• Sender reputation preservation: Neglecting bounce management, especially hard bounces, directly harms sender reputation, potentially leading to increased spam classifications or IP blocklistings (blacklistings). Learn more about how to measure bounce rate.
• Automated systems: Robust email platforms should have sophisticated automated bounce processing, eliminating the need for manual intervention and ensuring compliance with ISP requirements.
• Bounce codes: Understanding and classifying specific bounce codes is more important than the raw bounce email content for effective remediation. Our article on how ESPs manage bounces delves into this.
• Minimal retention: If bounce emails are received (which is less common with well-configured systems), any retention should be brief and strictly for specific diagnostic needs, not for a long-term archive.

Key findings

• Hard bounce action: Documentation consistently advises that hard bounced email addresses should be removed immediately from mailing lists because they represent permanent failures.
• Soft bounce retries: Soft bounces, indicating temporary issues, are often subject to a limited number of retries by ESPs before the address is suppressed. For instance, some recommend a maximum of six consecutive soft bounces before removal.
• Automated cleaning: Many email platforms automate the process of cleaning hard bounces and managing soft bounces, which means bounce emails rarely, if ever, require manual review in an inbox.
• Bounce rate targets: An acceptable bounce rate is typically cited as below 2%, with anything higher indicating the need for immediate attention to underlying list or sending practice issues.

Key considerations

• Impact on sender reputation: High bounce rates, especially from hard bounces, are a strong indicator of poor list hygiene and can severely damage sender reputation, leading to lower inbox placement and potential blacklisting (blocklisting).
• Classification accuracy: Accurately classifying bounce types is crucial for effective management. Hard bounces are permanent, while soft bounces are temporary issues that may resolve themselves.
• Compliance: Adhering to best practices for bounce management helps maintain compliance with ISP requirements and improves overall deliverability, as seen with Twilio's guidance.
• Data-driven decisions: Leveraging bounce data from SMTP logs or API responses is more effective for diagnostics and improving list quality than manually sifting through bounce emails, as outlined in the Server Fault discussion.