Why does bounce data from Drift Email differ from Hubspot's bounce data?

Key findings

• In-band vs. out-of-band bounces: Most email rejections happen in-band (during the initial SMTP handshake), which the sending ESP (like HubSpot) captures directly. Out-of-band bounces occur after the initial acceptance, often via a separate bounce message sent to the return path, which other tools might pick up.
• Return path handling: HubSpot likely sets the return path (MAIL FROM address) to its internal async bounce handler, meaning only HubSpot will receive these direct bounce notifications.
• Data accuracy: When HubSpot sends an email, it has 100% accurate data on delivery failures or bounces at the point of delivery. Discrepancies often indicate that the secondary tool (e.g., Drift) is interpreting data differently or receiving notifications from other sources.
• Secondary interpretations: Drift might be identifying bounces based on auto-replies or specific keywords in email responses, rather than formal bounce codes received by the ESP.
• Spam filters impact: Corporate spam filters can sometimes generate unique bounce-like messages or auto-replies that are not standard SMTP bounce codes, leading to different interpretations by various tools.

Key considerations

• Trust the ESP: For core bounce reporting, the data from your primary ESP (HubSpot in this case) is generally the most reliable as it has direct insight into delivery outcomes.
• Understand data sources: Investigate how each tool collects bounce data. HubSpot provides detailed email marketing metrics including bounce rates.
• Define bounce criteria: Be clear on what constitutes a 'bounce' for your team and how different platforms classify them, (e.g., hard vs. soft bounces). This can impact data comparison significantly.
• Actionable insights: Focus on the bounce data that helps you clean your lists and improve deliverability, rather than just raw numbers.

Key opinions

• Primary source reliability: Many marketers agree that the ESP (like HubSpot) provides the most accurate bounce reporting because they are directly involved in the email delivery process and receive immediate feedback on failures.
• Misinterpretation by third-party tools: There's a concern that tools like Drift might be misinterpreting auto-replies or other non-standard responses as bounces, leading to inflated or inaccurate bounce counts.
• Focus on deliverability: For marketers, the critical metric is whether an email was successfully delivered and not flagged as spam. Understanding the reasons behind different bounce reports is key to improving overall email deliverability.

Key considerations

• Reconcile data sources: Marketers should develop a strategy to reconcile bounce data from different tools, understanding what each platform is actually reporting and why there might be differences.
• Impact on sender reputation: Maintaining a low bounce rate is crucial for sender reputation. If a secondary tool reports high bounces not seen by the ESP, it's worth investigating to avoid potential blocklisting issues. An acceptable bounce rate is typically under 2%, as discussed by Dashly blog.
• Customer service notification: If the goal is to notify customer service of undeliverable emails, ensure the data source used for these notifications is highly reliable to prevent false alarms or missed critical bounces.

Key opinions

• ESPs are authoritative: Experts strongly assert that when an email is sent through an ESP like HubSpot, that ESP is 100% accurate regarding delivery and bounce outcomes because they directly handle the SMTP transaction.
• In-band rejections: Most rejections happen "in-band," meaning the recipient server immediately tells the sending server that the email cannot be delivered. These rejections do not involve the return path in a way that a third party would typically see.
• Drift's role: If Drift reports a bounce that HubSpot doesn't, it implies Drift is likely misinterpreting data or receiving information from a different, less reliable source, potentially due to its nature as an "epending" (email appending/processing) tool.
• Potential for misleading data: Experts caution that if an "epending" service reports bounces because its own mail sending activities are being blocked, this data is not useful for evaluating the deliverability of emails sent via the primary ESP.

Key considerations

• Prioritize ESP data: Always prioritize the bounce data provided by your main ESP for assessing email campaign performance and maintaining a healthy sending reputation. For HubSpot, this would be their native bounce reports.
• Investigate discrepancies: If a third-party tool reports significant bounce discrepancies, it warrants investigating the source and nature of these 'bounces' to ensure they are actual delivery failures and not misinterpretations. This is similar to how SNDS data can contradict deliverability.
• Return path understanding: A clear understanding of how the return path works and how ESPs use it for bounce processing is crucial when integrating with other tools.
• Evaluate tool accuracy: The reliability of a tool like Drift for bounce data should be evaluated critically, especially if its reports conflict with the ESP's accurate delivery logs, as highlighted by Word to the Wise regarding data accuracy in general.

Key findings

• SMTP standards: The Simple Mail Transfer Protocol (SMTP) dictates that recipient mail servers provide immediate feedback on delivery attempts. This is where most bounces are identified directly by the sending ESP.
• Return path (MAIL FROM): Bounce messages (Delivery Status Notifications) are sent to the address specified in the "MAIL FROM" command, often referred to as the return path or envelope sender. ESPs typically control this address for bounce processing.
• DSN messages: Delivery Status Notifications (DSNs) are standardized messages used to inform senders about delivery issues. While these are typically sent to the return path, not all email systems send them, or they may be delayed.
• Automated replies vs. bounces: Some systems send automated replies containing bounce-like text, but these are distinct from formal DSNs and can be misinterpreted by tools not designed for strict bounce processing.

Key considerations

• Protocol adherence: Ensure that any email sending or processing system adheres to established email protocols for bounce handling, such as RFCs, to ensure accurate data.
• Data aggregation: Recognize that different platforms may aggregate or display bounce data in varying ways, leading to apparent inconsistencies even if the underlying raw data is similar. This can be complex, as noted in Digital Marketing Institute's glossary.
• API limitations: Integration via APIs might not expose all granular bounce data that the primary ESP has internally, especially if the API is designed for contact syncing rather than deep deliverability metrics.