How to troubleshoot emails landing in spam despite passing DKIM, SPF, and DMARC?
Michael Ko
Co-founder & CEO, Suped
Published 8 Jul 2025
Updated 16 Aug 2025
7 min read
It can be incredibly frustrating when your emails land in spam, especially after you've diligently configured SPF, DKIM, and DMARC records and they're all passing authentication checks. You might expect smooth sailing once these foundational email authentication protocols are in place, but the reality is often more complex.
Passing SPF, DKIM, and DMARC is essential for email deliverability, yet it's only one piece of a larger puzzle. Internet Service Providers (ISPs) like Gmail and Outlook (and others like Yahoo) employ sophisticated filtering systems that consider hundreds of factors beyond just authentication. This guide explores the common reasons why your legitimate emails might still be flagged as spam and how to troubleshoot these issues effectively.
Even with perfect authentication, your emails can still land in the spam folder due to a variety of factors related to your sender reputation, email content, and recipient engagement. Authentication ensures the email is from who it claims to be, but it doesn't guarantee a good sender's standing or message quality. Think of SPF, DKIM, and DMARC as your passport, proving your identity, but other elements determine if you're welcome at the destination.
One primary reason is that mailbox providers maintain internal reputation scores for both sending IP addresses and domains. A low reputation score, whether for your IP or domain, can lead to inbox placement issues, regardless of your authentication status. This score is influenced by historical sending behavior, complaint rates, bounce rates, and engagement metrics.
Furthermore, content analysis plays a significant role. Spam filters meticulously examine email content for indicators of unsolicited bulk email. This includes specific keywords, formatting, image-to-text ratios, and links. A perfectly authenticated email with spammy content will likely still end up in the junk folder. Understanding how these filters work is crucial for improving your email deliverability.
Decoding sender reputation
Your sender reputation is arguably the most critical factor after authentication. It's a cumulative score that ISPs assign to your IP addresses and domains based on your past sending behavior. A poor reputation can cause your emails to be blocked or sent to spam, even if SPF, DKIM, and DMARC are all passing. This is why it's vital to monitor and maintain a healthy sender reputation.
One major indicator of a bad reputation is being listed on an email blocklist (or blacklist). These lists compile IP addresses and domains known to send unsolicited or malicious email. While many blocklists are public, some major ISPs maintain their own internal blocklists. Getting off a blocklist can be challenging, and it's always better to prevent being listed in the first place. You can learn more about what it means when your email is blacklisted in our detailed guide.
IP reputation: ISPs track the sending history of your IP address. High complaint rates, spam trap hits, or sending to invalid addresses can quickly damage this.
Domain reputation: This is tied to your sending domain. A consistent pattern of good sending practices builds trust over time, while abuse can swiftly destroy it.
Shared vs. dedicated IPs: If you're on a shared IP address, the sending behavior of other users on that IP can affect your deliverability, even if your own practices are stellar.
To gauge your domain's health, regularly check tools like Google Postmaster Tools, Microsoft SNDS (Smart Network Data Services), and other reputation services. These provide insights into your spam rate, IP and domain reputation, and DMARC failures.
Content and engagement factors
Even with a stellar sender reputation, your email content can trigger spam filters. ISPs analyze various aspects of your message, including keywords, formatting, and the ratio of images to text. Overly promotional language, excessive use of capitalization, or suspicious attachments can all contribute to your email being flagged.
Beyond content, recipient engagement is a huge signal for mailbox providers. If recipients consistently open, click, or reply to your emails, it signals that your emails are valued and legitimate. Conversely, low engagement rates, high unsubscribe rates, or frequent manual spam complaints can severely damage your inbox placement, even if your authentication checks pass.
Content pitfalls
Spam trigger words: Phrases like 'free money,' 'act now,' or 'guaranteed income' can quickly flag your email.
Poor formatting: Excessive images with little text, broken HTML, or too many fonts and colors can look suspicious.
Suspicious links or attachments: Links to unverified domains or unexpected attachments often trigger filters, as noted by Microsoft.
Email list hygiene is another critical area. Sending emails to invalid, inactive, or spam trap addresses can severely damage your sender reputation. Regularly cleaning your email list to remove stale or problematic addresses is crucial. This not only improves your deliverability but also reduces bounce rates and potential blocklisting (or blacklisting).
Leveraging analytics and local insights
To effectively troubleshoot, you need data. Google Postmaster Tools (GPT) is an invaluable, free resource for anyone sending to Gmail users. It provides insights into your IP and domain reputation, spam rate, feedback loop data, and DMARC failures. Setting up GPT for your sending domains is a non-negotiable step for serious email senders.
Similarly, Microsoft's SNDS and JMRP (Junk Mail Reporting Program) offer similar insights for Outlook/Hotmail addresses. Analyzing the data from these tools can pinpoint whether your issue is reputation-based, related to spam complaints, or stemming from authentication alignment problems (even if they're passing, alignment can be a nuanced issue as detailed in our guide on DMARC reports).
Finally, don't overlook local filtering. In some cases, especially when your own internal team receives emails in spam, the issue might be with your organization's internal email filters rather than the recipient's ISP. These local filters can have stricter rules or specific configurations that flag legitimate emails from your own domain. Examine the full email headers of a spam-folder email to understand the filtering path and specific reasons for its classification. This can provide clues specific to your internal environment.
Views from the trenches
Best practices
Actively monitor your IP and domain reputation using Google Postmaster Tools and other monitoring services.
Segment your audience and tailor content to ensure high engagement and relevance for your recipients.
Regularly clean your email lists to remove inactive or bouncing addresses and avoid spam traps.
Implement a double opt-in process for all new subscribers to ensure genuine interest and prevent spam complaints.
Test your emails before sending to catch any content that might trigger spam filters.
Ensure SPF, DKIM, and DMARC are not just passing but also properly aligned with your 'From' domain.
Common pitfalls
Solely relying on SPF, DKIM, and DMARC passing as a guarantee of inbox delivery, ignoring other factors.
Neglecting to monitor sender reputation, leading to silent degradation of deliverability over time.
Sending emails to unengaged recipients or purchased lists, which inflates complaint rates and spam trap hits.
Using generic or overly promotional language that triggers content-based spam filters.
Failing to review message headers for specific error codes or filtering reasons from ISPs.
Overlooking internal network or local email filters that might be causing delivery issues for internal recipients.
Expert tips
Prioritize recipient engagement metrics, as ISPs heavily weigh opens, clicks, and replies.
Use A/B testing for subject lines and content to optimize engagement and avoid spam folders.
Warm up new IPs or domains gradually to build a positive sending history with ISPs.
Set up feedback loops with major ISPs to quickly identify and address spam complaints.
Investigate BIMI implementation for enhanced brand trust and visual recognition, though it's not a direct spam fix.
Analyze DMARC reports thoroughly to identify authentication issues that might not be immediately obvious.
Marketer view
Marketer from Email Geeks says they send from Salesforce Marketing Cloud and their internal Gmail team is receiving some emails in the spam folder, even though SPF, DKIM, and DMARC are all passing and their deliverability vendor shows 100% deliverability.
2023-04-03 - Email Geeks
Marketer view
Marketer from Email Geeks notes that BIMI is not typically the cause of deliverability issues when emails are landing in spam, as it's more about branding than spam filtering.
2023-04-03 - Email Geeks
The path to inbox success
Passing SPF, DKIM, and DMARC is fundamental for email security and deliverability, but it's the beginning, not the end, of the journey to the inbox. Many other factors influence whether your emails bypass spam filters and reach their intended recipients.
By diligently monitoring your sender reputation, optimizing your email content, nurturing recipient engagement, and leveraging powerful analytics tools like Google Postmaster Tools, you can significantly improve your inbox placement. Remember that email deliverability is an ongoing process that requires continuous attention and adaptation to ISP filtering rules. For more general advice, consult our guide on why your emails fail.
Gmail and 
Outlook (and others like 
Yahoo) employ sophisticated filtering systems that consider hundreds of factors beyond just authentication. This guide explores the common reasons why your legitimate emails might still be flagged as spam and how to troubleshoot these issues effectively.
Microsoft SNDS (Smart Network Data Services), and other reputation services. These provide insights into your spam rate, IP and domain reputation, and DMARC failures.
Microsoft's SNDS and JMRP (Junk Mail Reporting Program) offer similar insights for Outlook/Hotmail addresses. Analyzing the data from these tools can pinpoint whether your issue is reputation-based, related to spam complaints, or stemming from authentication alignment problems (even if they're passing, alignment can be a nuanced issue as detailed in our guide on DMARC reports).
