Why is DMARC failing for my subdomain, and how does the Public Suffix List affect DMARC alignment?

Email marketer from StackOverflow shares that DMARC failures often stem from SPF and DKIM misalignment. Specifically, the 'header from' domain should align with the domain that passes SPF or DKIM. He shares that if your subdomain is sending emails, and the SPF record is misconfigured to include the top level domain, this may cause a problem if there are different providers sending from the subdomains. Additionally DMARC needs to be explicitly set to 'relaxed' alignment

Email marketer from Mailhardener explains that the Public Suffix List (PSL) can impact DMARC alignment. The PSL defines which domains are considered top-level domains. If a subdomain and its parent domain are both on the PSL, they are treated as separate entities, and DMARC alignment will fail unless explicitly configured to allow it.

Email marketer from Reddit shares that using relaxed alignment by setting the 'aspf' or 'adkim' tag in your DMARC record to 'r' can help fix some DMARC failures on subdomains, especially when using different sending providers for your subdomains. It makes DMARC more forgiving on subdomain mismatches in SPF and DKIM.

Email marketer from EasyDMARC shares that subdomain DMARC policies are crucial for ensuring proper DMARC alignment. If a subdomain policy is not explicitly set, it may default to a more restrictive setting, causing DMARC failures even if the parent domain passes. This can be especially problematic when using different sending sources for subdomains.

Email marketer from Email Security Forum explains that exceeding the SPF include limit (10 DNS lookups) is a common issue. When sending from multiple subdomains using various third-party services, it's easy to reach this limit, causing SPF checks to fail, consequently affecting DMARC. Use of SPF flattening might be necessary.

Email marketer from Valimail explains that managing DMARC for subdomains requires careful planning. Subdomain delegation or individual subdomain policies are important, especially if different teams or services use different subdomains. If subdomains use different sending infrastructures, each must be correctly configured with SPF and DKIM.

Email marketer from Email Geeks Forum explains that the user should check that their DMARC record isn't too restrictive for their subdomains. Setting the alignment mode to relaxed (r) and defining clear policies can prevent unexpected DMARC failures. Subdomains need specific attention to avoid overly strict rules.

Email marketer from Mailjet shares that DMARC requires you to explicitly set an authentication method to SPF or DKIM. If you are sending mail from a subdomain, you need to either set up SPF and DKIM on the subdomain itself, or on the root domain. Mailjet goes on to say that even if both are setup on the root domain, it is important that the correct method is being used on the subdomain for alignment checks.

Email marketer from Email Deliverability Forum mentions that forwarding can cause DMARC failures because it often breaks SPF alignment. When an email is forwarded, the original SPF record no longer matches the forwarding server's IP, leading to DMARC failing the SPF check. This affects subdomains and parent domains equally.

Email marketer from Email Deliverability Forum mentions that explicitly defining alignment settings in the DMARC record is critical. Ensure the 'aspf' and 'adkim' tags are correctly configured. Using 'r' (relaxed) is usually recommended for subdomains to allow for slight variations in domain alignment.

Expert from Word to the Wise explains not to add your domain to the Public Suffix List. He shares the PSL's original purpose was to isolate cookies and now it also affects email. Because it causes issues with email authentication he says not to request your domain be added to the list.

Expert from Word to the Wise explains how organizational domains, influenced by the Public Suffix List (PSL), impact DMARC. He shares that DMARC relies on the concept of organizational domains to determine if the domain in the 'From:' header aligns with the domain used for SPF or DKIM authentication. The PSL defines which domains are considered top-level domains, affecting how DMARC evaluates alignment. He also explains how DMARC alignment could fail unexpectedly if the sending and receiving domains aren't considered to be in the same organizational domain.

Expert from Email Geeks explains that when DMARC checks for alignment between two hostnames, it gets the TLD+1 for each hostname using the public suffix list, then compares them. But the TLD+1 for m.ghost.io using the older version of the public suffix list is m.ghost.io, not ghost.io.

Expert from Email Geeks suggests that the user can publish DMARC on ghost.io and the sub domains will inherit that policy.

Expert from Email Geeks explains that the DMARC failures are caused by ghost.io being in the Public Suffix List (PSL) at some point in the past. Because the PSL is cached, the problems persist even after removal from the list. He notes that the PSL was originally designed for browsers to ensure cookies were only accessible by the same website that set them. It was later adopted by the DMARC community for email alignment. He advises to mitigate it by either not using ghost.io for email or being very careful to never use the bare ghost.io hostname in email.

Documentation from Microsoft explains that a common reason for DMARC failure is incorrect SPF or DKIM setup on the subdomain. The domain used in the 'From:' header needs to align with the SPF or DKIM records for that specific subdomain. Misalignment, especially with third-party senders, can lead to DMARC failures.

Documentation from Google explains that DMARC failures can occur due to SPF or DKIM alignment issues. If the domain in the 'From:' header doesn't match the domain used to authenticate the email (either SPF or DKIM), DMARC will fail. Subdomain DMARC policies can also be misconfigured, leading to failures if not set up correctly to handle subdomain sending.

Documentation from RFC7489 explains that to determine if the domains in SPF, DKIM and the From header are aligned, an 'organizational domain' check is performed. This checks that each of these share the same organizational domain. If you are sending from a subdomain, this may be different from the From domain, causing DMARC to fail. You can configure these policies by using relaxed or strict policies. The public suffix list (PSL) impacts how the organizational domain is determined.

Documentation from AuthSMTP notes that for DMARC to pass for subdomains, SPF and DKIM records must be properly configured for those specific subdomains. It should also be confirmed that there are no conflicts with the parent domain's DMARC policy. Each subdomain needs its own set of valid authentication records.

Documentation from DMARC.org highlights that the PSL is used to determine the organizational domain for alignment purposes. If a domain is on the PSL, it is treated as a top-level domain for DMARC checks. This impacts subdomain alignment because the subdomain and parent domain may not align as expected if the PSL is in play.