Summary
Experts, email marketers, and documentation collectively highlight the importance of understanding bounce codes for email deliverability. While IANA provides a standard, ISPs often use custom codes. Bounce codes are categorized as 4xx (temporary failures) and 5xx (permanent failures). Furthermore, bounces are classified as hard, soft, or technical. Analyzing NDRs, monitoring bounce rates, and proactively removing bounced addresses are crucial. Utilizing bounce analyzer tools and ESP-specific documentation aids in effective bounce management. Proper bounce handling and feedback loops are also essential.
Key findings
- Code Categorization: Bounce codes are primarily categorized into 4xx (temporary) and 5xx (permanent) errors, with more detailed enhanced status codes available.
- Custom Codes: Many ISPs and filters use custom bounce codes, making standard documentation only partially useful.
- NDR Importance: NDRs (Non-Delivery Reports) provide vital information about email bounces, including SMTP codes, but explanations can be vague.
- Bounce Types: Bounces can be classified as hard, soft, or technical, indicating different causes of delivery failure.
- Management Importance: Proper management of bounces is crucial for maintaining a healthy sender reputation and improving email deliverability.
Key considerations
- ISP Variability: Be aware that bounce codes and explanations can vary significantly between ISPs and email providers.
- NDR Analysis: Carefully analyze NDRs and leverage external resources to understand bounce reasons.
- Enhanced Code Lookup: Utilize available documentation to decipher enhanced status codes for more specific error information.
- Proactive Removal: Proactively remove bounced email addresses from mailing lists to protect sender reputation.
- Tools & Documentation: Utilize bounce analyzer tools and refer to ESP-specific documentation for efficient bounce management.
- Feedback Loops: Implement and monitor feedback loops to improve deliverability and address bounce issues proactively.
What email marketers say
9 marketer opinions
Email marketers indicate that bounce codes (also known as SMTP error codes) are crucial for understanding why emails fail to deliver. These codes are generally categorized into 4xx (temporary failures) and 5xx (permanent failures). Different platforms and ESPs may provide more user-friendly explanations, and understanding these codes is essential for improving email deliverability and maintaining a healthy sender reputation. Strategies for managing bounces include differentiating between hard and soft bounces, using bounce analyzer tools, and proactively removing bounced addresses from mailing lists.
Key opinions
- Code Categories: Bounce codes are primarily categorized into 4xx (temporary) and 5xx (permanent) errors.
- Importance of Understanding: Understanding bounce codes is essential for improving email deliverability.
- User-Friendly Explanations: ESPs often provide user-friendly explanations of bounce codes beyond raw SMTP codes.
- Impact on Deliverability: Proper bounce management is crucial for maintaining a healthy sender reputation and improving deliverability.
- Range Meanings: 5xx codes generally indicate an issue with the recipient's address, while 4xx codes generally indicate a temporary server issue.
Key considerations
- Hard vs. Soft Bounces: Differentiate between hard bounces (permanent failures) and soft bounces (temporary issues) when managing your email list.
- ESP Documentation: Consult your ESP's specific documentation for the most accurate and user-friendly explanations of bounce codes.
- Bounce Analyzers: Consider using bounce analyzer tools to automate the categorization and interpretation of bounce codes.
- Proactive Removal: Proactively remove bounced email addresses from your mailing list to maintain a good sender reputation.
- Monitoring Bounce Rates: Actively monitor bounce rates and take action to minimize them to improve deliverability.
Marketer view
Email marketer from StackExchange explains that the 5xx range of codes generally indicates an issue with the recipient's address (doesn't exist, mailbox full, spam filter) while the 4xx codes generally indicates a temporary server issue.
1 Mar 2023 - StackExchange
Marketer view
Email marketer from ActiveCampaign answers by differentiating between hard bounces (permanent reasons like invalid addresses) and soft bounces (temporary issues like full inboxes), and explains their impact on email marketing strategies.
21 Sep 2022 - ActiveCampaign
What the experts say
5 expert opinions
Experts suggest that while resources like IANA exist, ISPs and filters often use their own unique bounce codes, making standard documentation less useful. NDRs contain valuable information, including SMTP error codes, but human-readable explanations might be vague. Enhanced status codes offer more detail but require external lookup. Proper bounce handling and feedback loops are also vital for maintaining deliverability.
Key opinions
- Custom Codes: ISPs and filters often use custom bounce codes beyond standard documentation.
- NDR Value: NDRs (Non-Delivery Reports) contain essential bounce information, including SMTP codes.
- Limited IANA Usefulness: Standard documentation like IANA may not fully reflect real-world bounce codes.
- Enhanced Codes Detail: Enhanced status codes provide more detailed explanations, but external lookup is necessary.
- Importance of Bounce Handling: Bounce handling and feedback loops are critical components of maintaining email deliverability.
Key considerations
- NDR Analysis: Analyze NDRs carefully to understand the reasons behind email bounces.
- ISP-Specific Codes: Be aware that bounce codes may vary across different ISPs and email providers.
- External Resources: Utilize external resources and documentation to decipher enhanced status codes.
- Feedback Loops: Implement feedback loops to manage bounces and improve sender reputation.
- Pardot's Blog Post: Review Pardot's blog post about bounce codes.
Expert view
Expert from Email Geeks shares a link to Pardot's blog post about bounce codes: <https://www.pardot.com/blog/bounce-codes/>.
1 Dec 2024 - Email Geeks
Expert view
Expert from SpamResource explains that enhanced status codes provide more detailed explanations than standard SMTP codes, structured as x.y.z, and that understanding these codes requires looking up their meanings in relevant documentation.
2 Nov 2024 - SpamResource
What the documentation says
5 technical articles
Documentation sources consistently point to SMTP error codes as the primary way to understand email delivery failures. These codes are typically divided into 4xx (temporary) and 5xx (permanent) categories. Additionally, bounce types are categorized as hard, soft, and technical, each representing different causes. Platforms like Amazon SES provide bounce notifications to aid in troubleshooting.
Key findings
- SMTP Error Codes: SMTP error codes are the standard method for explaining email delivery failures.
- 4xx vs 5xx: Bounce codes are categorized into 4xx (temporary errors) and 5xx (permanent failures).
- Bounce Types: Bounces are categorized as hard, soft, and technical, representing different causes of failure.
- Enhanced Codes: Enhanced mail system status codes provide standardized explanations for delivery failures.
- Platform Notifications: Platforms like Amazon SES provide bounce notifications with codes and descriptions for troubleshooting.
Key considerations
- Code Interpretation: Learn to interpret SMTP error codes to diagnose delivery problems.
- Temporary vs Permanent: Understand the difference between temporary and permanent failures when addressing bounce issues.
- Bounce Categorization: Classify bounces as hard, soft, or technical to implement appropriate solutions.
- Platform Tools: Utilize platform-specific tools and notifications to monitor and troubleshoot email delivery.
- IETF Standard: Reference IETF documentation for enhanced mail system status codes.
Technical article
Documentation from ietf.org specifies the enhanced mail system status codes that provide standardized explanations for delivery failures in SMTP.
13 Apr 2024 - ietf.org
Technical article
Documentation from AWS explains that Amazon SES sends bounce notifications containing information about why an email wasn't delivered, including bounce codes and descriptions, aiding in troubleshooting delivery issues.
19 Nov 2021 - AWS
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