Why are Mailgun logs showing emails from unexpected sources using my dedicated IP?

Key findings

• Log misinterpretation: The primary issue often stems from misinterpreting Mailgun's (or other ESPs') logs. What appears to be outbound traffic from your dedicated IP can actually be inbound messages being received by your domain via Mailgun's MX records.
• Inbound routing: Mailgun offers inbound routing capabilities, where your domain’s MX records point to Mailgun, allowing it to receive and process incoming emails for you. These incoming emails are then logged, and if forwarded, may appear to originate from your dedicated sending IP.
• Dedicated IP role: While dedicated IPs are crucial for building sender reputation for outbound mail, they can also be implicated in inbound mail processing if routing rules are configured.
• Spam and catch-alls: The appearance of spam-like from addresses often indicates that your domain is a target for inbound spam, which is being received and potentially filtered by a catch-all setup within your ESP.

Key considerations

• Verify log type: Always confirm whether the logs you are viewing are for outbound sending or inbound receiving. ESPs often have separate sections or indicators for these.
• Check mailgun routes: Review your configured Mailgun receiving routes in your control panel. If your MX records point to Mailgun, these routes dictate how incoming mail is handled.
• Understand dedicated IPs: Familiarize yourself with how dedicated IPs work within your ESP’s infrastructure, especially regarding their role in both sending and receiving processes.
• Implement DMARC: Ensure your domain has robust email authentication protocols like DMARC, SPF, and DKIM. This helps prevent unauthorized use of your domain and can provide clearer insights into legitimate vs. illegitimate traffic.
• Consult support: If unsure, provide detailed logs and context to your ESP's support team. They can help clarify log entries and ensure your configurations are correct.

Key opinions

• Initial alarm: Many marketers express immediate concern about unauthorized sending or spoofing when they see unfamiliar from addresses on their dedicated IP logs, fearing damage to their email deliverability.
• Log interpretation struggle: There's a common difficulty in distinguishing between outbound emails sent by their application and inbound emails being processed by the ESP (even if appearing to use the same IP in logs).
• Catch-all reliance: Marketers often rely on internal catch-all mechanisms to block unexpected inbound emails, providing a temporary sense of security but not addressing the root cause of the log entries.
• Support limitations: Some users report that initial support interactions with their ESP may not immediately identify the inbound routing as the cause, prolonging confusion.

Key considerations

• Educate on log types: Marketers should proactively understand the different types of logs provided by their ESP (e.g., Mailgun) and what each log entry signifies, especially the distinction between sent and received messages.
• Verify inbound configuration: If using an ESP for inbound email processing, regularly check your receiving rules to ensure they align with your expectations and security policies.
• Strengthen authentication: While not directly solving inbound spam, strong email authentication such as DMARC, SPF, and DKIM can help prevent your domain from being spoofed for outbound spam, improving overall security posture.
• Seek clarification: When logs are unclear, provide detailed screenshots and context to your ESP support. Sometimes, the initial explanation might need further probing to get to the core issue, as highlighted by Mailgun's own advice on debugging.

Key opinions

• Inbound traffic diagnosis: Experts quickly conclude that the logs are most likely displaying inbound email traffic (mail being received by the domain), which Mailgun then processes or forwards.
• Mailgun routes explanation: A key insight is that Mailgun offers receiving or inbound MX capabilities, which, when configured, cause incoming mail to pass through their system and be logged.
• Dedicated IP in forwarding: It is clarified that if an inbound route is set to forward a message, it will appear as sent from the Mailgun dedicated IP because Mailgun is effectively resending it to the final destination.
• Importance of DMARC: While not the primary cause of this specific log confusion, experts consistently emphasize DMARC as a crucial mechanism to prevent actual domain spoofing and gain visibility into all email traffic claiming to be from your domain. For further insights, refer to understanding DMARC reports.

Key considerations

• Thorough log analysis: Always conduct a comprehensive email deliverability audit that includes scrutinizing log headers and event types to differentiate between inbound and outbound activities.
• Review MX records: Check your domain's MX records to confirm where your incoming mail is being directed. If they point to your ESP, then inbound traffic processing is expected.
• Proactive DMARC deployment: Ensure you have a DMARC policy in place to gain visibility into all email traffic claiming to be from your domain, even if the primary issue here is log misinterpretation.
• Consult ESP experts: Do not hesitate to escalate issues with your ESP's support, providing them with as much detail as possible to get a precise diagnosis, especially for complex logging scenarios.
• Stay informed on blacklists: Continuously monitor your IP reputation on various blacklists and blocklists, as unexpected traffic, whether inbound or outbound, can affect your standing. This helps answer what happens when your IP gets blocklisted.

Key findings

• Dedicated IP primary purpose: Documentation confirms that dedicated IPs are primarily assigned for sending outbound email, allowing users to build and manage their own sender reputation independently, as explained in Mailgun's guide on dedicated IPs.
• Inbound processing: ESPs like Mailgun offer inbound mail processing (routes), where they receive emails for your domain via MX records. These incoming emails are then logged and can be forwarded to another address or processed by webhooks.
• Log variations: Documentation often details specific log event types (e.g., accepted, delivered) and their meaning, which can differ for outbound versus inbound email processing. This is a common aspect of debugging email issues with Mailgun logs.
• IP re-transmission in logs: If an inbound email is forwarded, the log entry for that forwarding action may show the email originating from the dedicated IP, as the ESP's system (including the dedicated IP) is used for the re-transmission.
• Importance of authentication: Documentation consistently stresses the importance of SPF, DKIM, and DMARC for both outbound email authenticity and protection against spoofing. Proper authentication helps to ensure that third-party emails are not mistakenly attributed to your domain.

Key considerations

• Consult official documentation: Always refer to your ESP's official documentation for precise definitions of log events and configurations. This is the most reliable source for understanding system behavior.
• Review receiving routes: If you are seeing unexpected traffic, review the receiving rules or routes in your ESP's control panel. Unintended configurations can lead to confusing log entries.
• Understand dedicated IP nuances: Recognize that a dedicated IP's function isn't solely limited to your explicit outbound sending. Its involvement in inbound processing or re-transmission should be understood to avoid false alarms.
• Implement strong security: Adhere to infrastructure security best practices provided by your ESP to minimize the risk of actual unauthorized use or misconfigurations.