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Summary

Understanding which SMTP bounce codes warrant immediate mailing list suppression is crucial for maintaining a healthy sender reputation and achieving optimal email deliverability. While hard bounces (typically 5xx codes) universally indicate permanent delivery failures requiring immediate removal, the handling of soft bounces (usually 4xx codes) is more nuanced. Different Email Service Providers (ESPs) and email platforms may classify errors differently and implement varying soft bounce tolerances. Effective bounce management involves a strategic approach to differentiate between temporary and permanent issues, ensuring that your suppression lists are accurate and prevent future deliverability problems. For a deeper dive into these classifications, you can read more about the difference between hard and soft bounces.

What email marketers say

Email marketers generally agree on the critical need to manage bounces effectively to protect sender reputation and optimize campaign performance. While hard bounces are universally seen as grounds for immediate removal, opinions on soft bounces vary, particularly concerning what constitutes a recoverable error. The consensus leans towards a tolerance policy for soft bounces, but with a clear threshold after which they should be treated as hard bounces and suppressed. This proactive approach helps prevent unnecessary sending to problematic addresses and improves overall inbox placement. Understanding these nuances is vital for anyone looking to manage their suppression lists effectively.

Marketer view

Email marketer from Email Geeks suggests that marketers with an export of bounce data could easily identify problematic email addresses and highlight any that stand out as red flags for suppression.

09 Oct 2019 - Email Geeks

Marketer view

Marketer from Marketing Platform highlights that there are three types of email bounce codes: hard, soft, or other, with individual error codes provided for each category for better classification.

20 Feb 2024 - MarketingPlatform

What the experts say

Email deliverability experts emphasize that while there are universal principles in bounce management, the specific classifications and handling can vary significantly between different ESPs. A core principle is that all 5xx SMTP errors signify permanent issues and mandate immediate suppression. However, experts highlight the nuanced nature of soft bounces, recognizing them as temporary errors that may recover, sometimes requiring sender action. The key lies in understanding that ESPs define and categorize bounces based on their internal documentation, influencing how issues like DNS failures or connection limits are treated. This complex landscape underscores the need for marketers to adapt their bounce management strategies to each sending environment. For more information, you can refer to expert advice on fixing bounce errors.

Expert view

Email deliverability expert from Email Geeks suggests that all 5xx errors are typically unrecoverable, meaning a single bounce is sufficient to take them right off the mailing list without further attempts.

09 Oct 2019 - Email Geeks

Expert view

Expert from SpamResource discusses the importance of maintaining a clean email list by promptly removing hard bounces, stating this is crucial for protecting sender reputation and avoiding email blacklists.

22 Apr 2024 - SpamResource

What the documentation says

Official documentation from various Email Service Providers and deliverability platforms provides concrete guidelines on how SMTP bounce codes should be interpreted and acted upon for mailing list suppression. These resources consistently define hard bounces as permanent errors that necessitate immediate removal to protect sender reputation. For soft bounces, documentation outlines specific retry policies and tolerance levels, after which a temporary issue can escalate to a permanent suppression. Understanding these documented rules is paramount for marketers and technical teams to build robust bounce management systems that align with industry best practices and ESP expectations. A key resource in this area is the SMTP Field Manual, which compiles raw SMTP server responses.

Technical article

Mailchimp documentation outlines their soft bounce tolerance policy, stating they allow seven soft bounces for an email address with no subscriber activity and up to 15 soft bounces for contacts with previous activity before converting it to a hard bounce and cleaning it from the audience.

09 Oct 2019 - Mailchimp

Technical article

Litmus documentation defines a soft bounce as a temporary delivery failure, indicating that while the current message was unsuccessful, there is a possibility that a future email to that address might be delivered successfully at a later date.

20 Oct 2016 - Litmus

11 resources

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