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Why There Are Lots of SPF Unaligned Emails: Understanding the Causes

When monitoring and reporting on DMARC (Domain-based Message Authentication, Reporting, and Conformance) for your email domain, you might notice a significant number of emails that fail SPF (Sender Policy Framework) alignment. This can be concerning, but it's essential to understand why this happens and why email forwarding is often the culprit.

What is SPF Alignment?

SPF is an email authentication method created to prevent email spoofing by checking if the sender's IP address is on an authorized list for the domain. For an email to pass SPF alignment under DMARC, the "From" domain (the visible sender) must match the domain verified by SPF.

Why Do Emails Fail SPF Alignment?

  1. Email Forwarding: This is the most common cause of SPF alignment failures. When an email is forwarded, the original sender’s IP address does not match the forwarding server’s IP address. Since the forwarding server is not listed in the original sender's SPF record, the forwarded email fails SPF checks.
  2. Mailing Lists: Similar to forwarding, emails sent to mailing lists and then distributed to members can fail SPF checks because the mailing list server is not authorized in the sender's SPF record.
  3. Incorrect SPF Records: Misconfigurations in SPF records can cause alignment failures. This includes missing IP addresses or ranges, syntax errors, or failing to include all legitimate sending sources.

Understanding Email Forwarding and SPF Failures

Email forwarding breaks SPF because the mechanism depends on the IP address of the sending server to verify the email. Here's how it works:

  1. Initial Send: An email is sent from an authorized sending server.
  2. Forwarding Server: The email is received by a server that then forwards it to another recipient.
  3. Recipient Server: The recipient's server performs an SPF check on the forwarding server's IP address, which is not listed in the original sender’s SPF record, resulting in an SPF failure.

The Impact of SPF Alignment Failures

While SPF alignment failures can suggest possible issues, it’s important to understand that they are not always evidence of malicious activity. Forwarded emails are valid but may fail SPF alignment because of the limitations of the SPF protocol when handling forwarded messages.

Solutions and Workarounds

  1. Implement DMARC with Relaxed Alignment: DMARC supports both strict and relaxed modes. Using relaxed alignment can decrease the number of alignment failures. In relaxed mode, the domain in the "From" address only needs to be a subdomain of the SPF domain, not an exact match.
  2. Use ARC (Authenticated Received Chain): ARC is a newer protocol designed to resolve issues like forwarding. It allows each entity handling the email to sign it, creating a chain of custody that the final recipient can verify.
  3. DKIM (DomainKeys Identified Mail) Alignment: Make sure DKIM is properly set up and aligned. DKIM signatures stay intact during forwarding, enhancing the effectiveness of SPF.
  4. Encourage Direct Delivery: Whenever possible, promote senders and recipients to bypass forwarding and send emails directly.

Conclusion

SPF alignment failures in your DMARC reports often occur due to email forwarding, which is a common and legitimate practice. Recognizing this can help you better interpret your DMARC reports and take suitable actions to improve email deliverability and security. Using DMARC with relaxed alignment, implementing ARC, and ensuring DKIM alignment can greatly reduce the effects of SPF alignment failures.

For further help with managing SPF alignment issues or any other questions related to DMARC monitoring, please contact our support team. We're here to assist you in navigating and improving your email authentication strategies.