Summary
It can be confusing when email authentication results from tools like G-Suite's Check MX Toolbox contradict the authentication results shown in email headers. If your email headers show DKIM and SPF passing, but a tool reports them as not set up, it often indicates a misunderstanding of how these tools operate versus the actual email delivery path.
Key findings
- Tool limitations: Many online tools (like MX Toolbox) perform a static DNS lookup for your domain's SPF and DKIM records. They do not simulate an actual email send or interpret email headers.
- Sender versus ESP: When sending emails through an Email Service Provider (ESP), your emails might be signed by both your domain's DKIM key and the ESP's own DKIM key. Similarly, the SPF record might only need to include the ESP's sending infrastructure, not necessarily Google's if you are using Google Workspace for mail but an ESP for marketing sends.
- Actual delivery path: Email headers reflect the actual authentication checks performed by the receiving mail server. If they show PASS, it means the receiving server successfully validated your email's SPF and DKIM.
- Misinterpretation: Tools may flag issues if they expect specific records (e.g., Google's SPF) for a domain managed by G-Suite, even if email is routed through a third-party ESP that handles authentication correctly.
Key considerations
- Prioritize email headers: The "Authentication-Results" section in your email headers is the definitive source for how receiving servers validated your email. If it passes, your setup is generally correct for those specific sends.
- Verify SPF record inclusions: Ensure your SPF record includes all legitimate sending sources, especially your ESP. A comprehensive guide on SPF alignment for Google Workspace can provide further insights.
- Understand DKIM delegation: If you're using an ESP, they often handle DKIM signing on your behalf. DomainKeys Identified Mail (DKIM) involves cryptographic signatures to verify sender identity, which ESPs facilitate for their clients.
- Cross-check with multiple tools: If one tool gives a suspicious result, try others or perform manual DNS lookups for your DKIM and SPF records. Sometimes, tools have cached data or specific configurations that lead to false negatives.
What email marketers say
Email marketers frequently encounter discrepancies between online testing tools and actual email header authentication results. This often leads to confusion, especially when their emails are successfully landing in inboxes while tools report issues. Marketers' experiences highlight the importance of understanding the context of email sending, such as whether an ESP is handling authentication or if mail is being sent directly from a G-Suite account.
Key opinions
- Conflicting information: Marketers are often puzzled when G-Suite's Check MX Toolbox indicates DKIM or SPF issues, but live email headers confirm a successful pass.
- Multiple DKIM signatures: It's common to see two DKIM signatures in email headers: one from the brand's domain and another from the ESP's domain.
- Tool reliability: There are reports of tools like MX Toolbox occasionally reporting records as non-existent when they are, in fact, properly configured and visible via other checkers.
- SPF return-path: Some marketers are unsure about the necessity of SPF records for their sending domain if a third-party ESP manages the return-path and bounces.
Key considerations
- Header review: Always thoroughly examine the "Authentication-Results" header, and potentially the "ARC-Authentication-Results" header, for concrete proof of SPF and DKIM validation.
- Domain alignment for DMARC: While email headers may pass SPF and DKIM, the overall DMARC authentication can still fail if there are alignment failures between the 'From' domain and the SPF/DKIM domains. Note that a p=NONE DMARC policy does not enforce failure, only monitors it.
- SPF for G-Suite: If you intend to send email directly from Google (e.g., via Gmail's SMTP using your custom domain), you absolutely need to add G-Suite's IPs to your SPF record.
- Tool versus reality: While tools are helpful, their static checks don't always reflect the dynamic nature of email authentication processes or ESP configurations.
Marketer from Email Geeks indicates confusion because their G-Suite Check MX toolbox shows "DKIM is not set up" and a red warning for SPF, while live email headers for sends to their Gmail account clearly state DKIM=PASS and SPF=PASS. They question whether this contradiction is expected.
Marketer from Email Geeks observes two DKIM signatures in their email headers: one aligning with their own domain and another with their ESP's domain. They confirm that all SPF, DKIM, and DMARC elements in the header appear to point to their domain and seem correct.
What the experts say
Email deliverability experts offer critical insights into why tools may present misleading authentication results. They emphasize the importance of distinguishing between how email authentication protocols like SPF and DKIM actually function in transit versus how static DNS checkers interpret domain configurations. Experts often find that the problem lies with the tool's methodology or specific expectations rather than an actual misconfiguration.
Key opinions
- Tool inaccuracy: Experts suggest that the MX Toolbox might be providing incorrect results or that the wrong test might have been requested, especially when manual lookups confirm a functional DKIM key.
- Functional DKIM: Even if a tool flags an issue, an expert can often confirm the DKIM key's functionality through direct checks, such as querying the specific DKIM selector in DNS.
- SPF for Google sending: If a domain is used to send emails directly through Google (e.g., via Google Workspace), its SPF record must explicitly include Google's sending servers.
- DMARC policy interpretation: A DMARC record with p=NONE is perfectly valid for monitoring purposes, and its presence or absence shouldn't cause DKIM/SPF failures in headers if they are otherwise correctly configured.
Key considerations
- Deep dive into headers: Experts often begin troubleshooting by examining the full email headers (both Authentication-Results and ARC-Authentication-Results) to confirm what receiving servers actually saw and validated.
- Sender domain context: It's crucial to understand which domain is being checked for SPF (the Return-Path) and DKIM (the d= tag) versus the visible 'From' address. These do not always align by default, impacting DMARC.
- Comprehensive SPF: Ensure that your SPF record accounts for all authorized sending services. A missing include statement for a legitimate sender is a common cause of SPF failures.
- DNS propagation: Remember that DNS changes take time to propagate globally. A tool might be querying an old DNS server, leading to outdated results, as discussed on Spam Resource.
Expert from Email Geeks suggests that the MX Toolbox might be inaccurate or that the user requested the wrong test. They performed a manual lookup of the DKIM key dkim1024._domainkey.comms.uwe.ac.uk and found it to be functional and correctly set up.
Expert from Email Geeks confirms that the DMARC record appears to be fine, although they personally prefer to include spaces between all settings for readability, noting that a semicolon is technically sufficient.
What the documentation says
Official documentation and technical resources explain the intricacies of email authentication protocols like SPF, DKIM, and DMARC. These sources clarify the distinct roles of each protocol, how they interact, and the mechanisms by which receiving mail servers validate them. Understanding these foundational principles helps demystify why discrepancies can arise between simple DNS lookup tools and the complex authentication processes that occur during email transmission.
Key findings
- DKIM purpose: DKIM (DomainKeys Identified Mail) uses cryptographic signatures to verify that an email was sent by an authorized sender and has not been tampered with in transit. It involves a public key published in DNS and a private key used by the sender.
- SPF function: SPF (Sender Policy Framework) allows domain owners to publish a list of authorized IP addresses that can send email on their behalf. Receiving servers check the sender's IP against this record.
- DMARC role: DMARC (Domain-based Message Authentication, Reporting, and Conformance) builds upon SPF and DKIM by providing a framework for domain owners to specify how receiving servers should handle emails that fail authentication, and to receive reports on authentication results.
- Header vs. DNS: Email headers provide the final authentication verdict from the receiving mail server. Online tools often perform simple DNS queries, which may not account for dynamic ESP configurations or full email processing.
Key considerations
- Correct DNS records: Ensure that your SPF and DKIM records are correctly published in your DNS. Website configuration documentation often provides step-by-step guides for this.
- Sender domain reputation: Even with perfect authentication, domain reputation plays a significant role in deliverability. New domains or those with a history of spam can experience blocklisting or inbox placement issues, as noted in domain reputation recovery guides.
- DMARC implementation: While p=none is a valid starting point, moving to more stringent DMARC policies like quarantine or reject requires careful monitoring of DMARC reports.
Documentation from Email on Acid states that a DKIM signature helps mailbox providers verify the sender's identity while simultaneously preventing phishing attacks, which are often characterized by email spoofing. This highlights DKIM's dual role in authentication and security.
Esecurity Planet documentation clarifies that DKIM only functions when email servers are specifically configured to check for DKIM signatures or utilize security tools that perform this validation. Servers have the option to bypass DKIM checks if they choose.
