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What does a 5.3.2 soft bounce error code mean when sending emails to Juno and NetZero?

Summary

The 5.3.2 soft bounce error code, often seen when sending emails to older internet service providers like Juno and NetZero, typically indicates that the recipient's mail system is temporarily unable to accept network messages. While a 5xx code usually signifies a hard bounce, this specific message suggests a temporary issue with the recipient's server rather than a permanent problem like an invalid address or a definitive spam blocklist entry. However, it can sometimes be a masked indication of an IP reputation issue or a mail block that is not explicitly stated. Understanding how email service providers manage bounce codes is crucial for effective email deliverability.

What email marketers say

Email marketers facing the 5.3.2 soft bounce error to Juno and NetZero often encounter a perplexing situation, as the error code suggests a hard bounce, yet the message implies a temporary block. Many marketers use ESPs like Pardot and need to understand if their shared or dedicated IP's reputation is at stake. The general consensus highlights the aging infrastructure of these ISPs, making deliverability to them a niche challenge. Marketers frequently consider the cost-benefit of troubleshooting these specific bounces versus simply removing the affected email addresses from their lists, especially given the typically small volume of such recipients.

Marketer view

Email marketer from Email Geeks notes a rise in 5.3.2 soft bounces to Juno and NetZero addresses, seeking advice on resolution for this unusual error code. They highlight that the volume, while high for them, is relatively small compared to their total sends.

18 Feb 2020 - Email Geeks

Marketer view

Email marketer from Email Geeks confirms that no emails were successfully delivered to the affected Juno or NetZero domains, indicating a complete block or persistent issue rather than sporadic delivery.

18 Feb 2020 - Email Geeks

What the experts say

Experts in email deliverability acknowledge that the 5.3.2 error for Juno and NetZero is unusual for a direct blocklist entry, often pointing to a temporary system failure rather than a clear spam classification. They emphasize the small scale of these ISPs, which often means limited direct support and unique bounce behaviors. Experts often advise checking official postmaster resources but also suggest that the low volume of affected addresses may make deep troubleshooting impractical. The distinction between a hard block and a transient system issue is critical for deciding on suppression strategies.

Expert view

Expert from Email Geeks queries if any emails were successfully delivered to the domains experiencing the 5.3.2 bounce, suggesting a need to verify the completeness of the delivery failure for a better diagnosis.

18 Feb 2020 - Email Geeks

Expert view

Expert from Email Geeks states that 5.3.2 is an unusual block response from Juno, which typically uses 550 access denied codes for their blocks. This implies the issue might not be a standard blocklist.

18 Feb 2020 - Email Geeks

What the documentation says

SMTP (Simple Mail Transfer Protocol) response codes are standardized to indicate the outcome of an email transfer attempt. Codes beginning with '5' are generally considered permanent failures (hard bounces), while '4' indicates a temporary failure (soft bounce). However, the specific sub-code and accompanying text provide crucial context. A 5.3.2 error, 'system not accepting network messages,' while falling under the permanent failure category, often refers to a generic configuration issue or temporary overload on the receiving server, rather than a specific content or reputation block. Internet standards (RFCs) outline these codes, but individual mail servers may implement them with slight variations or use generic messages for complex issues, particularly older or smaller ISPs.

Technical article

RFC 3463, section 3.2, describes the 5.3.2 status code as 'System not accepting network messages,' clarifying that this usually indicates the recipient's system is either configured incorrectly or temporarily overloaded and cannot accept the current connection.

10 Mar 2003 - RFC 3463

Technical article

The official SMTP specification, RFC 5321, reiterates that a 5xx series response signifies a permanent failure, advising the sender to stop attempting to deliver the message without modification. This underscores the need for senders to eventually suppress such addresses.

01 Oct 2008 - RFC 5321

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