Why do Salesforce Marketing Cloud hard bounces show a different recipient email address while engagement continues?

Key findings

• Asynchronous bounces: The most common explanation is that an email was initially accepted by the recipient's server and then forwarded, with the bounce occurring asynchronously from the final, invalid destination. This is discussed in depth by Digital Marketing on Cloud.
• Return-path integrity: With naive email forwarding, the return-path (envelope sender) often remains unchanged. This allows the final recipient's mail server to send a bounce notification directly back to the original sender (SFMC), bypassing the forwarding server.
• VERP encoding: SFMC utilizes Variable Envelope Return Path (VERP) encoding. This includes unique identifiers in the return-path, enabling it to link these asynchronous bounces to the specific subscriber key, even if the reported bounced address is different.
• Engagement metrics: Observed opens and clicks can still occur because the original email address might remain active and accessible (e.g., via webmail), or the email might be forwarded to multiple active addresses alongside the invalid one. Alternatively, these engagements could be attributed to spam filter activity pre-delivery.

Key considerations

• Bounce management: SFMC's automated bounce management is designed to handle these cases, marking the subscriber as held after a certain number of hard bounces, regardless of intermittent engagement. For more details, see our guide on Salesforce Marketing Cloud bounce handling.
• Data interpretation: While unusual, these mixed signals (bounces and engagement) are often a normal, if complex, part of email deliverability. Understanding why emails hard bounce then open is crucial for accurate list hygiene.
• Diagnostic limitations: Although more detailed data from SFMC could offer deeper insights, the underlying cause is likely forwarding, and the practical outcome (subscriber eventually being suppressed) remains the same.

Key opinions

• Baffling bounces: Marketers frequently find it confusing when hard bounces show different recipient email addresses than the one originally targeted.
• Forwarding suspicions: The primary hypothesis among marketers for this behavior is typically email forwarding. They often wonder how a bounce from a forwarded address could propagate back to SFMC.
• Engagement paradox: The existence of concurrent opens and clicks from the original subscriber, despite bounces, adds to the mystery and raises questions about true engagement vs. automated activity.
• Data discrepancies: Marketers note the difficulty in finding the bouncing email address within their subscriber lists, indicating it's not a direct recipient in SFMC.

Key considerations

• Impact on deliverability: While SFMC's automation usually handles hard bounces, understanding how to manage hard bounced addresses is key for maintaining list hygiene.
• Data integrity: It's important to differentiate between true subscriber engagement and automated actions by mail servers. The Trailhead community discusses hard bounce handling.
• Troubleshooting: If a seemingly valid email address hard bounces, it often requires investigating the full bounce message and understanding the specific domain configurations.

Key opinions

• Forwarding is likely: Experts strongly concur that email forwarding is the most probable cause for a hard bounce originating from a different email address than the one initially targeted.
• Asynchronous bounces explained: When mail is forwarded naively, the original return-path doesn't change. If the final forwarded destination rejects the email, it sends an asynchronous bounce directly to the sender (SFMC).
• VERP's role: SFMC's VERP-encoded return-path is critical for it to capture and match these rejections from forwarded messages back to the specific subscriber. More information on VERP is available here.
• Engagement variations: Engagement (opens/clicks) can still occur if the email is forwarded to multiple active addresses, is readable via webmail at the initial domain, or if spam filters are pre-scanning emails.
• BCC functionality: SFMC’s BCC functionality can also cause similar broad bounce issues if the BCC address is invalid.

Key considerations

• Trust bounce automation: For the most part, SFMC's built-in bounce management should handle these issues automatically, suppressing the problematic subscriber over time.
• Forensic data is often unnecessary: While SFMC likely captures enough metadata for a full diagnosis, it may not be worth the effort for small numbers, as the action taken (suppression) remains the same. Understanding why emails fail is paramount.
• Context matters: Knowing the domains involved (e.g., a professional association domain forwarding to a generic MBP) can confirm the forwarding hypothesis. Regularly reviewing email deliverability issues can help identify patterns.

Key findings

• Hard bounce definition: Official documentation specifies that a hard bounce occurs when the recipient email address is invalid or does not exist, indicating a permanent rejection.
• SFMC handling: Salesforce Marketing Cloud typically sets a subscriber status to 'Held (Undeliverable)' after a certain number of hard or soft bounces, preventing future sends to that address. More insights on getting SMTP bounce messages are available.
• Recipient server influence: Whether a hard bounce occurs also depends on the settings and specifications of the recipient's email server, which can influence how bounces are generated and reported.
• Bounce reason codes: Bounce messages, such as '5.1.1 User unknown', provide specific reasons for rejection, even if they originate from a forwarded path.

Key considerations

• Understanding bounce data: Documentation often emphasizes the importance of reviewing bounce data for insights into deliverability and list health.
• Managing undeliverable subscribers: Best practices for data management in SFMC include handling held subscribers to ensure efficient sending. This can also help when you are seeing a spike in hard bounces later in your campaigns.
• Impact on sender reputation: High hard bounce rates, even if indirectly caused by forwarding, negatively affect sender reputation and can lead to emails being blocked or blacklisted.