Why are some emails failing DMARC checks even with correct SPF and DKIM alignment, and how can I troubleshoot it?

Email marketer from StackOverflow explains that one possible cause of SPF failures is having too many 'include:' mechanisms in your SPF record, exceeding the 10 DNS lookup limit. This can cause SPF to return a 'permerror' result, leading to DMARC failure.

Email marketer from SuperUser notes that if DMARC is set up for the main domain, but subdomains are sending emails without proper SPF and DKIM records, then DMARC failures are likely to occur. Ensure that all subdomains sending emails are correctly configured or use a wildcard DMARC record.

Email marketer from EasyDMARC shares that common causes of DMARC failure, despite valid SPF and DKIM, include email forwarding, changes made by email list servers, and issues with the alignment between the 'From:' domain and the domains used for SPF and DKIM.

Email marketer from Twitter recommends validating the DMARC configuration by using online DMARC testing tools to verify that the records are correctly set up and to simulate email flows to check for any potential issues.

Email marketer from MXToolbox User recommends analyzing DMARC aggregate reports, which provide insights into the sources of email and their authentication results. This allows you to identify unauthorized senders, misconfigurations, and potential spoofing attempts.

Email marketer from GlockApps suggests setting up DMARC monitoring to get aggregate reports of SPF, DKIM, and DMARC results from various ISPs. This helps in identifying and troubleshooting DMARC failures over time.

Marketer from Email Geeks suggests asking the DNS provider if they do rate limiting, especially if not using Route53.

Email marketer from URIports advises using DMARC reports to identify the source of DMARC failures. These reports can show which emails are failing SPF or DKIM, and from which IPs, helping to pinpoint configuration issues or unauthorized sending sources.

Email marketer from EmailonAcid highlights that SPF and DKIM passing alone is not sufficient; DMARC requires 'alignment'. This means the domain in the 'From:' header must match the domain used in the SPF and DKIM records. Misalignment can cause DMARC failures.

Email marketer from Mailhardener explains that mailing lists often modify emails in transit which can cause DKIM signatures to break. Even if SPF is aligned, DMARC will still fail if DKIM fails. They recommend configuring mailing lists to rewrite the 'From:' address to the mailing list domain to align with SPF.

Email marketer from Reddit shares that intermittent DMARC failures, even with correct SPF and DKIM, could be due to DNS propagation issues or temporary DNS server outages. They suggest checking DNS records periodically and ensuring DNS servers are reliable.

Expert from Email Geeks suggests checking that all nameservers are in sync, DNS entries are correct, and DNS resolvers are responding quickly. DNS failures can occur due to UDP's lack of error correction.

Expert from Email Geeks explains that a small percentage of emails failing DMARC is not unexpected and is part of how DMARC works, even if everything is configured correctly.

Expert from Spam Resource responds discussing the importance of setting up DMARC feedback loops and also mentions the difficulties in resolving all DMARC failures perfectly due to factors like forwarding and variations in mail server configurations.

Expert from Word to the Wise explains that list servers often rewrite email headers, which breaks DKIM signatures. While SPF might still pass if the list server is authorized to send on behalf of the domain, the DKIM failure can cause DMARC to fail. He suggests that list owners should re-sign messages.

Documentation from Google Workspace Admin Help explains that forwarding can cause DMARC failures. When an email is forwarded, the SPF record will fail because the email is no longer coming from an authorized server. If the forwarder also modifies the message content, the DKIM signature will fail as well. This can happen even if the original email passed DMARC checks.

Documentation from Microsoft highlights that DMARC failures can occur even with valid SPF and DKIM when intermediate mail servers don't properly handle email authentication. ARC (Authenticated Received Chain) helps preserve email authentication results across multiple hops, but if ARC validation fails, DMARC can also fail.

Documentation from dmarc.org details that even with correct SPF and DKIM configuration, DMARC can still fail if there are issues like mail forwarding that breaks SPF or DKIM signatures, or if the email's 'From:' address does not match the domain used for SPF and DKIM.