Summary
Deliverable users can be incorrectly marked as undeliverable due to a confluence of issues related to ESP definitions and interpretations, server configurations, temporary rejections, and list hygiene. ESPs often create artificial hard/soft bounce distinctions. The actual reason for bounces often needs to be deciphered from rejection messages. Factors such as smaller provider reliability, greylisting, aggressive filtering, and temporary blocks all contribute. Accurate bounce processing, regular list cleaning, email authentication, and monitoring are critical for maintaining deliverability.
Key findings
- ESP Bounce Definitions: Hard and soft bounce distinctions are largely defined by ESPs, not inherent email protocols.
- Rejection Message Insight: Analyzing rejection messages gives insight into specific bounce reasons.
- Provider Reliability: Smaller providers can contribute to increased bounce rates.
- Misclassification of Temporary Issues: Temporary rejections (e.g., greylisting) are often misclassified as permanent failures.
- List Hygiene Impact: Outdated email addresses and typos contribute significantly to bounces.
- Filtering and Blocklists: Aggressive spam filters and blacklists may incorrectly flag valid addresses.
- Server Misconfigurations: Server misconfigurations can cause false hard bounces.
Key considerations
- Review Rejection Messages: Thoroughly examine rejection messages to understand underlying issues.
- Maintain List Hygiene: Implement regular list cleaning and validation practices.
- Evaluate ESP Bounce Process: Understand and potentially advocate for changes to ESP bounce processing.
- Implement Email Authentication: Use SPF, DKIM, and DMARC to improve deliverability and trust.
- Monitor Bounce Rates: Regularly monitor bounce rates and investigate unusual patterns.
- Address Server Issues: Resolve server misconfigurations or temporary blocks.
- Use Feedback Loops: Implement feedback loops to address deliverability problems proactively.
What email marketers say
9 marketer opinions
Deliverable users experiencing hard bounces and being incorrectly marked as undeliverable can stem from various factors. These include invalid or outdated email addresses, recipient server issues, temporary blocks from firewalls, and misclassification of temporary issues by ESPs due to aggressive bounce rules or overly aggressive spam filters. Issues with sender reputation, spam traps, and greylisting can also contribute. Email verification tools aren't foolproof, and temporary delivery issues can still cause bounces.
Key opinions
- Invalid Addresses: Outdated email addresses and typos contribute to hard bounces.
- Server Issues: Recipient server problems and temporary blocks can cause bounces.
- ESP Misclassification: ESPs may incorrectly classify temporary issues as hard bounces due to aggressive rules.
- Sender Reputation: Poor sender reputation and spam traps can lead to deliverability problems.
- Filtering Issues: Overly aggressive spam filters may misclassify legitimate emails.
- Verification Limitations: Email verification tools are not always accurate.
Key considerations
- List Hygiene: Regularly clean and update email lists to remove invalid addresses.
- Bounce Monitoring: Monitor and manually review bounce reports to identify misclassifications.
- Email Authentication: Implement SPF, DKIM, and DMARC protocols to improve deliverability.
- Reputation Monitoring: Monitor sender reputation and avoid spam traps.
- Feedback Loops: Implement feedback loops to address deliverability issues.
- Deliverability Testing: Test email deliverability with various mailbox providers to identify potential problems.
Marketer view
Email marketer from Reddit shares that ESPs may incorrectly classify temporary issues as hard bounces due to aggressive bounce rules. It is important to monitor and manually review bounce reports.
22 Feb 2023 - Reddit
Marketer view
Email marketer from GlockApps explains that while not a direct cause, landing in spam traps or blocklists can indirectly cause deliverable users to get hard bounces. Regular list hygiene and sender reputation monitoring are key.
23 May 2023 - GlockApps
What the experts say
11 expert opinions
Deliverable users are marked as undeliverable and receive hard bounces due to a complex interplay of factors. ESPs often 'make up' the distinction between hard and soft bounces, influencing how rejections are classified. The classification can be inaccurate due to ESP misinterpretations, greylisting being mistaken for permanent failures, smaller mailbox providers' reliability, or bounce processing errors. Blocklists, USER_NOT_FOUND classifications, and overly aggressive filtering also contribute. Examining rejection messages directly from mailbox providers is crucial to understanding the actual reasons for the bounces and whether the ESP's classification is accurate. In some cases, these are temporary issues. Understanding the ESP's hard bounce process and potentially advocating for changes may be necessary, especially when working with platforms like Responsys.
Key opinions
- ESP Bounce Definitions: The distinction between hard and soft bounces is often ESP-defined and not inherent to email protocols.
- Rejection Message Importance: Rejection messages provide valuable insights into the reasons for bounces and whether an ESP has misclassified them.
- Provider Reliability: Smaller mailbox providers may be less reliable and contribute to bounce issues.
- Classification Inaccuracy: ESPs can misinterpret temporary issues (e.g., greylisting) as permanent failures.
- Blocklist Influence: Smaller providers might use shared blocklists, leading to false positives.
- Overly Aggressive Filtering: Overly aggressive filtering by ESPs and mailbox providers can result in misclassifications.
- USER_NOT_FOUND Caveats: USER_NOT_FOUND classifications are often accurate but can still be misleading in certain situations.
Key considerations
- Examine Rejection Messages: Always review the actual rejection messages from mailbox providers to understand the specific reasons for bounces.
- Understand ESP Processes: Familiarize yourself with your ESP's hard bounce process and how they classify rejections.
- Advocate for Change: If necessary, advocate for changes to your ESP's hard bounce process to minimize misclassifications.
- Consider Provider Differences: Be aware that smaller mailbox providers may have different deliverability characteristics.
- Monitor Blocklists: Check if your sending IP is on any shared blocklists.
- Investigate USER_NOT_FOUND: Thoroughly investigate USER_NOT_FOUND errors, even if they seem definitive.
- Evaluate Bounce Processing: Ensure that bounce processing systems are accurately interpreting server responses.
Expert view
Expert from Email Geeks suggests talking to Responsys about making changes to their hard bounce process. Mentions that some folks might be able to help craft an argument for the changes.
17 May 2022 - Email Geeks
Expert view
Expert from SpamResource explains that sometimes the interpretation of bounce messages by the sending server is incorrect, leading to an address being marked as a hard bounce when it's actually a temporary issue.
30 Mar 2022 - SpamResource
What the documentation says
3 technical articles
According to documentation from SparkPost, Mailgun and Amazon SES, hard bounces typically indicate permanent reasons for email delivery failure, like non-existent addresses or blocked senders. However, server misconfigurations, outdated information, and temporary filtering rules can lead to legitimate addresses being incorrectly flagged as hard bounces. Monitoring bounce notifications and investigating patterns are crucial for identifying and addressing these false positives.
Key findings
- Hard Bounce Definition: Hard bounces generally indicate permanent delivery failures.
- Misconfiguration Errors: Server misconfigurations can lead to false hard bounces.
- Temporary Issues: Temporary server problems or filtering can cause valid addresses to bounce.
- Monitoring Importance: Monitoring bounce notifications is crucial.
Key considerations
- Investigate Bounce Patterns: Investigate patterns in bounce notifications to identify potential misconfigurations.
- Review Server Settings: Regularly review server settings and filtering rules to ensure accuracy.
- Handle Temporary Errors: Implement systems to handle temporary server errors without permanently removing addresses.
Technical article
Documentation from Mailgun clarifies that hard bounces occur when an email is permanently undeliverable due to reasons like a non-existent address or a blocked sender. However, server misconfigurations can sometimes cause temporary issues to be incorrectly classified as hard bounces.
25 Apr 2024 - Mailgun
Technical article
Documentation from Amazon SES details that while hard bounces usually indicate permanent issues, temporary server problems or filtering rules can occasionally cause valid addresses to bounce. Monitoring bounce notifications and investigating patterns is important.
1 Aug 2023 - Amazon Web Services
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