Why is Gmail showing a warning message despite passing DMARC?
Michael Ko
Co-founder & CEO, Suped
Published 24 Jul 2025
Updated 17 Aug 2025
6 min read
It can be incredibly frustrating to see a warning message on your Gmail messages, especially when you've diligently set up DMARC, SPF, and DKIM and your reports show 100% success rates. The message, often stating, "Be Careful with this message. The sender hasn't authenticated this message so Gmail can't verify that it actually came from them," can be quite alarming for legitimate senders. You might be left wondering, what's going on if DMARC is passing?
This issue is more common than you might think, and it typically points to factors beyond the basic DMARC pass/fail. While DMARC verifies that your email is authorized, Gmail's sophisticated algorithms look at a much broader set of signals to determine trustworthiness and inbox placement. These signals include sender reputation, content quality, and even how your DNS records are performing over time. It's not just about passing authentication, it's about building and maintaining trust.
When you encounter this warning, it suggests that while your email passed the technical authentication checks, other elements might be raising flags. It's a nuanced problem requiring a deeper look into your email sending practices. Understanding these underlying issues is key to resolving the warning and ensuring your emails consistently land in the inbox.
One of the most common reasons for Gmail warning messages, even with DMARC passing, is an issue with alignment. DMARC relies on either SPF or DKIM to be aligned with the RFC 5322 From: header. While your DMARC reports might show a pass, it's possible that only one of these (e.g., DKIM) is aligning, and Gmail's internal heuristics might prefer or expect both.
If your SPF isn't aligning, or if it's set up in a way that sometimes fails or leads to inconsistent DNS lookups, Gmail's system could flag the message. For instance, if your SPF record uses an excessive number of DNS lookups (exceeding the 10-lookup limit), it could intermittently fail verification, leading to warnings even if most of the time it passes.
Similarly, issues with DKIM key rotation, incorrect selector usage, or modifications to the email content in transit (perhaps by an intermediate mail server or Security Email Gateway, SEG) could cause DKIM to fail authentication, even if it appears to be configured correctly. Gmail's strictness means any deviation can trigger a warning.
Checking SPF alignment
Ensure your SPF record includes all IP addresses or domains authorized to send email on behalf of your domain. Pay close attention to the Return-Path (or Envelope-From) domain, as this is what SPF authenticates against. For SPF to align, the Return-Path domain must match your From: header domain or be a subdomain thereof.
Checking DKIM alignment
Your DKIM signature should verify the domain in your From: header. If your email service provider uses a different signing domain, it may pass DKIM but fail DMARC alignment unless specific steps are taken to ensure alignment with your sender domain. Ensure no DKIM body hash mismatch failures are occurring, which can lead to authentication failures.
Sender reputation and content flags
Beyond authentication protocols, Google's email systems heavily weigh sender reputation. Even if your SPF, DKIM, and DMARC records are impeccable, a poor sender reputation can trigger warnings or send emails to spam. Gmail (and Yahoo Mail) considers various factors when assessing reputation.
Your IP address reputation, domain reputation, and the content of your emails all play a role. If your sending IP or domain has previously been associated with spam, or if you're suddenly sending a high volume of emails without a proper warm-up, this can negatively impact your reputation. Similarly, if your emails frequently receive spam complaints, this will quickly degrade your standing with mailbox providers.
The content itself can also be a culprit. Overly promotional language, suspicious links, attachments, or even unusual formatting can trigger Gmail's spam filters, resulting in a warning. Mismatched sender domains, where the friendly From: address doesn't match the underlying sending domain, can also be a red flag.
What is it?
An email forwarding service receives an email and then resends it to another address. This process can break SPF and DKIM authentication because the forwarding server's IP isn't authorized in the original sender's SPF record, and the content might be altered, invalidating DKIM.
Impact on warnings
Even if your initial send passes DMARC, a forwarded email might fail authentication on the receiving end. This can result in a warning message for the recipient, as Gmail sees a discrepancy despite the original DMARC pass.
What to do?
Minimize forwarding: Encourage direct sends where possible. If forwarding is necessary, be aware of its limitations.
Check DMARC reports for forwarded email: Look for aggregate reports that show authentication failures from legitimate sources due to forwarding.
Clean your list: Remove inactive or invalid email addresses to reduce bounce rates and spam complaints.
Other technical considerations
Even with perfect authentication and a good reputation, intermittent issues can arise from DNS. DNS propagation delays, caching problems, or even temporary outages with your DNS provider can lead to inconsistent authentication results. If Gmail attempts to verify your DMARC, SPF, or DKIM records and encounters a temporary DNS failure, it might default to a warning state, even if the issue resolves moments later.
This is particularly true for shared IP addresses. If you're sending through an email service provider (ESP) that uses shared IPs, the actions of other senders on those same IPs can influence your deliverability. If another sender on a shared IP ends up on an email blacklist (or blocklist), it could temporarily affect all senders using that IP, including you. Monitoring your IPs for blocklist listings is crucial.
Finally, the type of DMARC policy you've implemented can also play a role. While a 'p=none' policy won't cause rejections, a more restrictive 'p=quarantine' or 'p=reject' policy, if misconfigured or if there are intermittent authentication issues, could lead to warnings or even emails being sent to spam. This is why a gradual transition to stronger DMARC policies is advised.
Views from the trenches
Best practices
Always maintain a clean email list to minimize bounces and spam complaints, which significantly boost your sender reputation.
Use an email service provider (ESP) that offers dedicated IPs for higher sending volumes to isolate your reputation.
Implement both SPF and DKIM with strict alignment to your 'From' domain for robust email authentication.
Common pitfalls
Overlooking SPF alignment issues, where the return-path domain does not match the 'From' header domain.
Ignoring DMARC aggregate reports, which contain crucial data about authentication passes and failures.
Sending emails with inconsistent content or sudden spikes in volume, triggering spam filters.
Expert tips
For intermittent warnings, check your DNS resolver logs for any transient errors or timeouts during authentication checks.
Ensure your email sending platform isn't modifying email headers in a way that breaks DKIM or DMARC alignment.
Consider if mail forwarding is involved on the recipient's side, as this often breaks SPF and DKIM for legitimate emails.
Expert view
Expert from Email Geeks says DNS failures, inconsistent DNS results, or mail forwarding are common culprits for these warnings.
2024-05-17 - Email Geeks
Marketer view
Marketer from Email Geeks says they confirmed that forwarding wasn't the issue in their case, but DKIM-alignment was the only one set up, so they are now trying to set up SPF alignment as well.
2024-05-17 - Email Geeks
Navigating Gmail's advanced filters
Seeing a Gmail warning message despite passing DMARC can be perplexing, but it underscores that email deliverability is a multi-faceted challenge. It's not just about meeting the minimum authentication requirements, but about building a holistic picture of trustworthiness for mailbox providers. Focus on a combination of technical accuracy, consistent sender reputation management, and high-quality content.
By proactively addressing potential issues with SPF and DKIM alignment, monitoring your domain and IP reputation, refining your email content, and understanding how external factors like mail forwarding can impact authentication, you can significantly reduce these warnings. This comprehensive approach helps ensure your legitimate emails reach the inbox without unnecessary flags, maintaining your brand's credibility and communication effectiveness.
