Summary
Useful bounce data for email marketing goes beyond the simple categories of 'hard' and 'soft' bounces. While these classifications provide a basic understanding, true deliverability insights require more granular information directly from SMTP responses and detailed delivery status notifications (DSN). The primary challenge lies in the current simplification of bounce data by many Email Service Providers (ESPs), which, while aiming for user-friendliness, often obscures critical technical details necessary for advanced troubleshooting and optimization.
Key findings
- Inadequate data: Many ESPs offer insufficient bounce data, typically limited to hard and soft classifications, which are often vaguely defined and lack actionable detail.
- Need for raw data: Deliverability professionals require access to the full, unedited SMTP response codes and delivery status notifications (DSN) to accurately diagnose bounce reasons.
- Beyond classifications: Specific information like the bounce domain, the mail transfer agent (MTA) sending the bounce, and even the sending IP and DKIM algorithm (especially for SHA-1 refusals) are crucial.
- Non-standard responses: Some mailbox providers, like Yahoo with its TSS0* codes, provide helpful yet non-standard indicators that can offer deeper insights.
- Operational challenges: The simplification of bounce data by ESPs is often a compromise to reduce customer support burden, as raw data can be confusing for most users.
Key considerations
- Data granularity: Marketers should push for ESPs to provide more detailed bounce data, even if it requires a deeper dive into reports or APIs. Understanding the definitions of bounce types is a starting point.
- Impact on sender reputation: Accurate bounce data helps identify issues that negatively impact sender reputation, such as consistently hitting invalid addresses or blocklists.
- List hygiene: Detailed bounce data is essential for maintaining a clean email list, identifying invalid addresses quickly, and reducing future bounces.
- Strategic adjustments: Understanding specific bounce reasons allows marketers to make informed decisions, such as adjusting sending volume, segmenting lists, or refining content.
What email marketers say
Email marketers often express frustration with the lack of detailed bounce data provided by ESPs. While they understand the need for simplicity for general users, the absence of granular information like exact SMTP responses can hinder their ability to effectively diagnose and resolve deliverability issues. Many feel that the current 'hard' and 'soft' bounce categories are overly simplistic and disconnect from the reality of complex email delivery challenges. They seek data that allows for proactive problem-solving rather than reactive measures after reputation damage has occurred.
Key opinions
- Simplistic categorization: The common 'hard' and 'soft' bounce classifications provided by ESPs are often seen as too basic and unhelpful for genuine deliverability analysis, as they simplify complex underlying issues.
- Desire for raw data: Many marketers wish ESPs would provide the exact, unedited SMTP response codes for a deeper understanding of bounce reasons.
- Actionable insights: They believe that better data would enable them to take more effective actions, rather than just seeing generic red or yellow indicators.
- Beyond SMTP: There's a call for information on the specific domain or mail transfer agent (MTA) responsible for sending the bounce.
Key considerations
- Improved list hygiene: More precise bounce reasons would allow marketers to clean their email lists more effectively, removing problematic addresses and improving overall engagement.
- Proactive issue resolution: With better data, marketers could identify emerging deliverability issues earlier, before they escalate into significant inbox placement problems or blacklisting.
- Segmented strategies: Understanding specific bounce types helps in tailoring marketing strategies for different segments, potentially reducing bounces for certain campaigns.
- Vendor accountability: Marketers are looking for ESPs to be more transparent about the data they collect and how it can be accessed, enabling better partnership in deliverability management. Consider best practices for email verification.
Marketer view
Email marketer from Email Geeks suggests that the current definitions of soft and hard bounces by some ESPs are out of touch with reality. These definitions often lack the nuance required for effective deliverability management, leading to confusion and misinterpretation of critical delivery issues.
Marketer view
Email marketer from Mailmunch advises that a non-delivery report (NDR) is received when an email bounces, indicating it never reached the recipient's inbox. Understanding the specifics of these reports is vital for diagnosing why emails are not being delivered.
What the experts say
Email deliverability experts highlight a crucial distinction between what basic marketers need and what professionals require from bounce data. While simplified categories help general users avoid being overwhelmed, experts emphasize the necessity of raw, unedited SMTP responses and detailed DSN (Delivery Status Notification) data. They point out that ESPs often manage delivery errors internally, but truly effective deliverability management for clients requires access to the underlying reasons for bounces, enabling proactive pattern identification and issue resolution. This includes specifics like the exact SMTP response, the sending IP, and even the DKIM algorithm.
Key opinions
- Raw SMTP responses: Experts advocate for the inclusion of the entire, unedited SMTP response in bounce data. This provides the most precise reason for delivery failure, which is essential for diagnosing complex issues and identifying SMTP bounce logs.
- Post-acceptance bounce data: For bounces occurring after initial acceptance (DSN messages), the full message should be available in a structured format like XML or JSON.
- Sending environment details: Knowing the specific sending IP and the DKIM algorithm used (especially in light of SHA-1 deprecation) can be critical for troubleshooting deliverability issues.
- ESPs' responsibility: True ESPs should proactively monitor DSN data and take action, helping clients improve sending rather than just providing raw data that could overwhelm them and increase support requests.
- User confusion: While raw codes are useful for experts, they can confuse most users, leading to increased customer service demands. This is a key reason ESPs simplify the data.
Key considerations
- Advanced analysis: Access to comprehensive bounce data allows experts to identify subtle patterns and root causes that simplified data would completely miss. This enables more effective bounce management.
- Collaboration with ESPs: Clients should inquire about their ESP's approach to bounce data and whether advanced options or a deliverability team are available to interpret this data.
- Tailored suppression: Detailed bounce reasons enable more intelligent suppression rules, such as differentiating between temporary issues and permanent blockages, impacting soft bounce suppression logic.
- Educating clients: Experts must find ways to explain complex bounce data in an understandable format to clients, translating technical responses into actionable strategies.
Expert view
Email expert from Email Geeks suggests that the ultimate goal for useful bounce data is the entire, exact, and unedited SMTP response. This level of detail is paramount for diagnosing complex deliverability issues and understanding the precise reasons for email rejections.
Expert view
Email expert from Word to the Wise advises that understanding the nuances of bounce types, beyond simple hard and soft, is crucial for maintaining good sender reputation. Generic classifications can obscure the real underlying problems.
What the documentation says
Official documentation and industry standards, while providing frameworks for email delivery, often focus on the technical protocols rather than the practical reporting needs of marketers. RFCs define SMTP responses and DSNs, outlining the precise codes and messages associated with delivery failures. However, they don't prescribe how ESPs should summarize or present this data to end-users. This gap often leads to the simplified 'hard' and 'soft' bounce categories, which, despite being standard internal ESP classifications, lack the granular detail specified in the underlying protocols that deliverability professionals need to fully understand and action bounce events.
Key findings
- RFC standards: RFCs (Request for Comments) define the technical specifications for email, including SMTP response codes (e.g., 5xx for permanent errors, 4xx for temporary errors) and DSN formats, which are the foundation for bounce reporting.
- Categorization variations: While RFCs provide codes, the interpretation into 'hard' and 'soft' categories is left to individual ESPs, leading to inconsistencies in how bounces are classified and reported. These classifications are fundamental to how a bounce domain's reputation is understood.
- Detailed error messages: DSN messages (post-acceptance bounces) provide detailed information, including specific diagnostic codes and human-readable explanations, often in a multipart format that requires parsing.
- Authentication failures: Bounce data may also indicate issues with email authentication protocols like SPF, DKIM, and DMARC, particularly if the bounce message refers to policy failures or authentication checks.
Key considerations
- Parsing raw data: To gain truly useful insights, it may be necessary to parse raw SMTP responses and DSNs directly, rather than relying solely on ESP summaries.
- Understanding RFCs: Familiarity with RFCs (e.g., RFC 5321 for SMTP, RFC 3464 for DSNs) can help in interpreting detailed bounce messages and their implications for deliverability.
- Vendor capabilities: When choosing an ESP, inquire about their capabilities to provide comprehensive bounce data, including raw logs or structured DSN information, rather than just high-level summaries.
- Proactive monitoring: Even with simplified data, consistent monitoring of bounce rate trends is essential, as sudden spikes can indicate significant deliverability problems, such as a blocklist listing.
Technical article
Documentation from RFC 5321 (SMTP) specifies that the SMTP server should return a reply code indicating the status of the delivery attempt. These codes (e.g., 2xx for success, 4xx for temporary failure, 5xx for permanent failure) are the fundamental building blocks of bounce data.
Technical article
Documentation from RFC 3464 (DSN) outlines the Delivery Status Notification (DSN) format, detailing how mail systems report delivery status. A DSN message contains structured information, including the original recipient, the status code, and a diagnostic code, providing detailed reasons for non-delivery or delayed delivery.
Related resources
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