Why are my emails landing in spam even though they pass SPF, DKIM, and DMARC?
Matthew Whittaker
Co-founder & CTO, Suped
Published 1 May 2025
Updated 18 Aug 2025
8 min read
It can be incredibly frustrating to find your emails consistently landing in spam folders, especially when you've diligently set up your authentication protocols, SPF, DKIM, and DMARC. These protocols are the bedrock of email security, verifying your identity and preventing spoofing. They tell receiving mail servers that your emails are legitimately from your domain. However, passing these checks is a necessary, but not always sufficient, condition for inbox delivery.
Email deliverability is a complex ecosystem, influenced by a multitude of factors beyond just authentication. While SPF, DKIM, and DMARC confirm your email's origin, they don't guarantee its trustworthiness in the eyes of an inbox provider (ISP). These providers, like Google and Microsoft, employ sophisticated spam filters that analyze hundreds of signals to decide where an email should land. If you are experiencing issues even with passing authentication, it is possible your emails are being filtered for other reasons.
The challenge often lies in understanding these additional criteria. Many email marketers and system administrators face this dilemma. It is not uncommon for messages, even critical transactional emails or important communications, to be misdirected.
One of the most significant factors influencing email deliverability, beyond authentication, is your sender reputation. Both your sending IP address and your domain have reputations. These reputations are built over time based on your sending practices and recipient engagement. If you are using a new domain or IP, it likely has a neutral reputation, which means ISPs are cautious and may send your emails to spam by default until a positive sending history is established. This is why IP warming and domain warming are critical for new senders.
Factors that can severely damage your sender reputation include high spam complaint rates, high bounce rates (especially to non-existent addresses), sending to purchased lists, and getting listed on a blocklist (or blacklist). Even if you pass SPF, DKIM, and DMARC, a poor reputation signals to ISPs that your mail, while authenticated, may not be desired by recipients. Many ISPs have their own internal reputation scores, which they do not publicly share, that influence deliverability. These scores are highly sensitive to user feedback and engagement.
You can monitor your domain's health through tools like Google Postmaster Tools, which provides insights into your sender reputation, spam rates, and DMARC reports for Gmail users. Similarly, Microsoft's Smart Network Data Services (SNDS) offers similar data for their properties. Regularly checking these dashboards can help you identify if your reputation is an issue.
The impact of a damaged reputation
A damaged sender reputation can lead to emails being quarantined or outright rejected, even if they pass all authentication checks. This is especially true for transactional emails, which are expected to be highly reliable. If your transactional emails are landing in spam, it's a strong indicator of a reputation problem.
Beyond technical configurations, the content of your emails and how recipients interact with them play a crucial role. Spam filters analyze email content for characteristics commonly associated with spam, such as:
Spammy keywords: Words like 'free,' 'guarantee,' 'win,' 'cash,' or excessive use of exclamation points.
Poor formatting: Large fonts, unusual colors, excessive images with little text, or broken HTML.
Suspicious links: Links to suspicious domains, or a high number of links relative to the text content.
Attachments: Certain file types or suspicious attachment names can trigger filters.
Recipient engagement is equally, if not more, important. ISPs monitor how subscribers interact with your emails. Positive engagement, like opens, clicks, replies, and adding your address to their address book, boosts your reputation. Conversely, negative engagement, such as deleting emails without opening them, moving them to spam, or unsubscribing, can severely damage it. Even a low spam rate might be misleading if your overall engagement is poor, as ISPs may still route your emails to the junk folder. This is particularly relevant for marketing emails that rely heavily on subscriber interaction.
Regularly cleaning your email lists to remove inactive or invalid addresses is crucial to maintaining good engagement metrics and avoiding spam traps. If you're seeing your emails go to spam despite a low spam rate, poor engagement might be the underlying cause.
Content best practices
Clear subject lines: Avoid misleading or overly promotional phrases.
Balanced text-to-image ratio: Ensure sufficient text content.
Legitimate links: Only link to reputable domains.
Easy unsubscribe: Provide a clear and functional unsubscribe option.
Engagement strategies
Maintain list hygiene: Regularly remove inactive or unengaged subscribers.
Segment your audience: Send targeted content to increase relevance.
Encourage interaction: Ask recipients to reply or add you to contacts.
Monitor engagement metrics: Track opens, clicks, and spam complaints.
Hidden blocklists and DNS issues
While you might check common public blocklists (or blacklists) and find your IP or domain clean, there are many private and internal blocklists used by ISPs. These lists are not publicly accessible and are often based on real-time data and proprietary algorithms. Getting listed on such a blocklist can severely impact deliverability, even with perfect authentication. Sometimes, your shared IP address might be on a blocklist because of another sender's poor practices. Our blocklist monitoring service helps identify if you're on these lists.
Beyond blocklists, subtle DNS misconfigurations or issues that don't directly cause SPF, DKIM, or DMARC failures can still raise red flags for spam filters. For example, a missing or incorrect PTR record (reverse DNS) can make your sending server seem less legitimate. Similarly, issues with certificate transparency (CERT records), while not directly tied to email authentication, can indicate a lack of proper domain setup.
It's also worth noting that some DMARC policies, even if technically passing, might not be strong enough. If your DMARC policy is set to p=none, it tells receiving servers to only monitor emails that fail authentication, not to block them. While a good starting point for DMARC implementation, this policy offers no protection against malicious spoofing and does not enhance deliverability. To improve deliverability and protect your domain, you should aim for a p=quarantine or p=reject policy once you're confident in your authentication setup. Check out our guide on DMARC policy examples for more details.
Even after passing all initial authentication and reputation checks, emails can still be filtered based on the recipient's personal preferences or the ISP's advanced content filtering. Some ISPs, especially major ones like Gmail and Outlook (Office 365), use sophisticated machine learning algorithms that analyze user behavior and content in real-time. If a high percentage of users mark your emails as spam, even if they initially land in the inbox, future emails may be routed directly to the junk folder for other recipients. This dynamic filtering can be particularly challenging to troubleshoot. Our article on troubleshooting Gmail spam offers more insights.
This advanced filtering is why even emails from trusted sources, like Google Calendar invites or internal communications from Google Workspace business accounts, can sometimes end up in spam if the overall sending patterns or domain reputation have been negatively impacted. A sudden surge in mail volume, even legitimate, can sometimes trigger these filters if not properly warmed up. It's not just about what you send, but how you send it.
If a large volume of spammy emails were sent from your domain (even if by a malicious actor), it creates a lasting impression on these sophisticated filters. It takes consistent positive sending behavior over time to rebuild that trust. This period of recovery can be lengthy, especially for B2B senders with lower, less frequent sending volumes compared to B2C marketers. This is why it's crucial to address the root cause of the reputation damage and implement long-term fixes.
The comprehensive view of email deliverability
Deliverability issues are rarely due to a single factor. While SPF, DKIM, and DMARC are crucial, they are part of a larger picture. Think of it like this: authentication gets your email past the bouncer at the club's entrance, but your behavior inside (content, engagement, reputation) determines if you stay or get kicked out.
For a holistic approach to email deliverability, consider all aspects of your sending strategy. You can also use an email deliverability tester to diagnose potential problems.
Views from the trenches
Best practices
Monitor your domain and IP reputation regularly using Postmaster Tools for major ISPs.
Implement a slow and consistent sending ramp-up (warming) for new domains or IPs.
Segment your audience and personalize content to improve engagement metrics.
Common pitfalls
Overlooking low sending volume as a cause for poor reputation, especially in B2B contexts.
Assuming authentication (SPF, DKIM, DMARC) is the only factor influencing inbox placement.
Ignoring content quality and recipient engagement metrics in deliverability troubleshooting.
Expert tips
Focus on consistent, positive engagement to slowly rebuild domain trust after a hit.
Check for any less common DNS records or configurations that might be missing or incorrect.
For B2B senders, even small negative signals can have a disproportionate impact due to lower volume.
Expert view
Expert from Email Geeks says a key factor for emails landing in spam, even with valid SPF, DKIM, and DMARC, is often low domain reputation. It can be particularly challenging to fix for low-volume senders, like many B2B operations.
2022-04-08 - Email Geeks
Expert view
Expert from Email Geeks says managing reputation is significantly harder in B2B environments compared to B2C, where higher volumes and more frequent interactions allow for quicker adjustments to sending strategies.
2022-04-08 - Email Geeks
Moving forward
While passing SPF, DKIM, and DMARC is fundamental for email deliverability, it's just the starting point. Achieving consistent inbox placement requires a holistic approach that considers your sender reputation, email content quality, recipient engagement, and adherence to ISP-specific guidelines. Regularly monitor your deliverability, respond to feedback loops, and commit to consistent, positive sending practices. By addressing these often-overlooked factors, you can significantly improve your chances of reaching the inbox.
Google and 
Microsoft, employ sophisticated spam filters that analyze hundreds of signals to decide where an email should land. If you are experiencing issues even with passing authentication, it is possible your emails are being filtered for other reasons.
Gmail and Outlook (Office 365), use sophisticated machine learning algorithms that analyze user behavior and content in real-time. If a high percentage of users mark your emails as spam, even if they initially land in the inbox, future emails may be routed directly to the junk folder for other recipients. This dynamic filtering can be particularly challenging to troubleshoot. Our article on troubleshooting Gmail spam offers more insights.
