Why are my emails being marked as spam even with good domain reputation?
Michael Ko
Co-founder & CEO, Suped
Published 5 Jul 2025
Updated 19 Aug 2025
10 min read
It can be incredibly frustrating to see your emails land in the spam folder when you know your domain reputation is good, especially according to tools like Google Postmaster Tools. Many factors influence email deliverability, and domain reputation, while crucial, is just one piece of a complex puzzle. I often hear this concern from senders who have invested in maintaining a clean domain history, yet still struggle to reach the inbox.
The truth is, email service providers (ESPs) and mailbox providers (MBPs) like Gmail and Microsoft Outlook use a sophisticated array of signals to decide where an email should land. A good domain reputation indicates trustworthiness, but other elements can still trigger their spam filters. This means that even if your domain is clean, other aspects of your sending behavior or email content could be raising red flags.
Understanding these additional factors is key to diagnosing and fixing inbox placement issues. It’s not always an obvious problem, and sometimes, a seemingly minor detail can have a significant impact on your deliverability, steering your messages away from the primary inbox and into the junk folder.
Content quality and user engagement
Even with a stellar domain reputation, the content of your emails plays a critical role in whether they reach the inbox or are diverted to spam. Spam filters analyze various elements within your email, from subject lines to body text and embedded links, looking for patterns commonly associated with unsolicited mail. If your content appears spammy to the filters, it can override a positive domain reputation.
Low engagement rates are another major red flag. If recipients consistently ignore, delete, or mark your emails as spam, mailbox providers interpret this as a sign that your content isn't valuable, regardless of your domain's overall standing. This negative feedback loop can gradually erode your sender score with specific ISPs, even if your broader domain reputation remains high in generalized tools like Google Postmaster Tools. This is especially true if you are sending to inactive or unengaged users.
Maintaining a healthy list and sending engaging content are fundamental to good deliverability. High bounce rates, especially to invalid or non-existent addresses, can also severely impact your sender reputation, even if your domain is otherwise in good standing. Spam traps, which are email addresses used by ISPs to catch senders who don't maintain clean lists, are particularly detrimental. Hitting these can lead to immediate blocklisting (or blacklisting), regardless of your overall domain reputation.
Spam complaints: Even a small number of direct spam complaints can significantly harm your standing with mailbox providers, triggering filters to redirect future emails to the junk folder.
Engagement metrics: Low open rates, low click-through rates, and high unsubscribe rates tell ISPs that your content isn't desired by recipients. This can lead to increased filtering.
Spam trap hits: Landing on a spam trap can instantly damage your sender reputation, regardless of your domain's general standing.
Hidden technical and authentication issues
Even if your domain's reputation appears solid, subtle or advanced technical misconfigurations can cause your emails to be marked as spam. While you may have basic Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM) records set up, issues like alignment failures or improper Domain-based Message Authentication, Reporting & Conformance (DMARC) policies can still lead to deliverability problems.
A common overlooked aspect is the DMARC policy itself. Even if your SPF and DKIM pass, if your DMARC policy is set to p=none, it signals to receiving servers that you're not taking an active stance against email spoofing, which can affect trust. Similarly, a DMARC record that fails to align correctly with your sending domain can lead to emails being filtered.
Moreover, problems with reverse DNS (PTR records) or issues with your mail server's IP reputation, even if your domain is clean, can cause emails to be flagged. Some ISPs maintain their own internal blocklists (blacklists) that aren't publicly accessible and can be triggered by various proprietary signals, including content, sending patterns, or previous recipient complaints. These subtle technical issues are often invisible to standard domain reputation checks.
Your sending infrastructure, even if it has a good domain reputation, can be a silent culprit. While your domain itself might be trusted, the IP address (or range of IP addresses) from which your emails originate might not share the same pristine reputation. This is especially true if you are using a shared IP address where other senders' poor practices could be impacting your deliverability. Many mailbox providers consider both domain and IP reputation when evaluating incoming mail.
Even with a good domain reputation, if the IP address you are sending from has a poor reputation or is listed on a blocklist (or blacklist), your emails are likely to be filtered. This can happen if the IP was previously used by a spammer or if it has recently experienced a sudden spike in volume or complaints. Receiving servers use these blocklists to quickly identify and reject email from known problematic sources, irrespective of the sending domain's overall standing. It is essential to monitor both your domain and IP reputation consistently.
Furthermore, a sudden change in your sending volume or patterns can trigger spam filters. If you suddenly send a large volume of emails from a domain that typically sends less, even with a good reputation, it can appear suspicious and lead to throttling or junk folder placement. This is why proper IP warming strategies are critical for new IPs or when significantly increasing sending volume. Without it, your emails might go to spam even if your domain reputation is established and positive.
Domain reputation and IP reputation
Your domain's reputation is about your brand's trustworthiness. Your IP's reputation is about the trustworthiness of the specific server sending your email. Both are crucial for deliverability, but a problem with one can impact the other's effectiveness, even if it appears healthy.
How they interact
Shared IPs: If you're on a shared IP, other senders' bad practices can affect your IP reputation, even if your domain is clean. This can lead to your emails being marked as spam.
Dedicated IPs: While you have more control, a new dedicated IP needs careful warming up. Rushing sends can immediately harm its reputation, pulling down your domain's effective deliverability.
List quality and acquisition practices
Even if your domain's reputation is pristine, your email list quality can be the primary reason for emails ending up in spam. Sending to unengaged, invalid, or improperly acquired contacts signals to mailbox providers that you might be engaging in questionable sending practices, regardless of your overall domain standing. A high number of bounces, even if handled, suggests an unkempt list.
Spam traps are a significant threat to list quality. These are email addresses designed to catch spammers. Hitting a spam trap can severely damage your sender reputation and lead to immediate blacklisting (or blocklisting) by ISPs. Even if your domain reputation is otherwise good, a single spam trap hit can cause significant deliverability problems. Regular list hygiene and using a double opt-in process are crucial to avoid these pitfalls.
Furthermore, if your subscriber acquisition practices are not transparent, or if recipients feel they didn't explicitly opt-in, they are more likely to mark your emails as spam. This negative feedback directly impacts your sender reputation with individual mailbox providers, even if your domain looks good in aggregate reports. It is important to remember that subscriber consent is paramount to email deliverability.
Good list practices
Double opt-in: Require subscribers to confirm their subscription, ensuring genuine interest.
Regular cleaning: Remove unengaged or invalid email addresses regularly to reduce bounces and spam trap hits.
Clear unsubscribe: Provide a clear and easy way for recipients to opt out, reducing spam complaints.
Bad list practices
Purchased lists: These often contain spam traps and unengaged users, leading to high complaints and blocklisting.
Single opt-in only: Can result in accidental sign-ups or malicious subscriptions, increasing bounce and complaint rates.
Ignoring bounces: Continued sending to invalid addresses signals poor list management and hurts your reputation.
Content and external domain reputation
I find that even when your primary domain reputation is good, problems can arise from other domains or links within your email content. If you're linking to a website with a poor reputation or including images hosted on a domain associated with spam, this can trigger filters. Mailbox providers assess the reputation of all linked domains, not just the sending domain, when determining an email's trustworthiness.
Furthermore, some spam filters, like SpamAssassin's Razor2, focus heavily on content fingerprints and recurring spammy creative elements. If your email shares content patterns that have been previously identified as spam by other users, even if your domain is clean, these filters can mark your email. This isn't necessarily a sign of a bad domain reputation, but rather a content-specific issue that needs addressing.
Finally, certain email clients or niche ISPs might employ unique filtering rules or have lower thresholds for what they consider spam. While your emails might sail through Gmail's filters, they might get caught by a more stringent filter at another provider. This highlights the importance of testing your emails across a wide range of mailbox providers to identify isolated deliverability issues. Each provider has its own criteria, and a good domain reputation doesn't grant universal immunity.
Addressing content and external link issues
Review all links: Ensure all hyperlinks and image sources within your email point to reputable, healthy domains.
Content analysis: Avoid 'spammy' words, excessive capitalization, and overly promotional language. Balance text with images.
A/B test: Experiment with different content variations to see what performs best in terms of inbox placement.
Views from the trenches
Best practices
Regularly monitor your content for 'spammy' keywords and patterns.
Implement double opt-in for all new subscribers to ensure consent.
Routinely clean your email lists of inactive or invalid addresses.
Verify all links and hosted images point to reputable domains.
Warm up new IPs or domains gradually to build reputation.
Common pitfalls
Over-reliance on Google Postmaster Tools for overall deliverability status.
Ignoring specific ISP feedback or niche blocklists (like Razor2).
Sending to purchased or unverified email lists, leading to spam trap hits.
Sudden, large increases in sending volume without proper warming.
Using misleading subject lines or overly promotional content.
Expert tips
Analyze engagement rates beyond opens and clicks, including replies and forwards.
Segment your audience and tailor content to increase relevance and engagement.
Pay close attention to user feedback loops (FBLs) from mailbox providers.
Ensure your DNS records (SPF, DKIM, DMARC) are perfectly configured and aligned.
Use email deliverability testing tools to diagnose specific inbox placement issues.
Expert view
Expert from Email Geeks says Razor2 is a hobby project and unlikely to cause deliverability problems with major providers like Gmail and Microsoft. The issues you're seeing are more likely due to convergent evolution of spam filters, meaning different filters are flagging similar content for the same reasons, not because major providers are using Razor2 data.
2021-06-18 - Email Geeks
Expert view
Expert from Email Geeks says that while Cloudmark might have acquired parts of Razor2, it doesn't mean there's data sharing or common code between them and major email providers. If your content appears spammy to one filter, other filters looking for similar heuristics will also likely detect it independently.
2021-06-19 - Email Geeks
Key takeaways
While a strong domain reputation is foundational for email deliverability, it's clearly not the sole determinant of inbox placement. The complex interplay of content quality, precise technical configurations (beyond basic SPF/DKIM), underlying IP reputation, and the health of your email list all play equally vital roles. To consistently reach the inbox, a holistic approach is required, constantly monitoring and optimizing each of these elements.
I find that achieving excellent deliverability means looking beyond surface-level metrics and diving deep into the nuances of how mailbox providers interpret your sending behavior. By addressing potential issues in content, authentication, IP reputation, and list hygiene, you can significantly improve your chances of consistently landing in the inbox, even when your domain reputation already appears solid.
Gmail and 
Microsoft Outlook use a sophisticated array of signals to decide where an email should land. A good domain reputation indicates trustworthiness, but other elements can still trigger their spam filters. This means that even if your domain is clean, other aspects of your sending behavior or email content could be raising red flags.
