Why are my emails going to spam in Gmail even though everything seems technically correct?
Michael Ko
Co-founder & CEO, Suped
Published 13 Jul 2025
Updated 17 Aug 2025
8 min read
It is incredibly frustrating when you are diligently sending emails, ensuring all the technical configurations like SPF, DKIM, and DMARC are perfectly set up, and yet your messages still end up in the spam folder in Gmail. This can feel like hitting a brick wall, especially when you receive feedback that your emails are being flagged as "similar to messages identified as spam in the past." This particular message from Gmail indicates that the issue goes beyond basic authentication, delving into content, sender behavior, and reputation.
Many senders assume that once their email authentication is correctly implemented, their deliverability issues should vanish. However, Gmail and other major mailbox providers employ sophisticated algorithms that evaluate numerous factors beyond just the technical setup. My experience shows that these factors often relate to how your emails are perceived by recipients and the overall health of your sending practices.
I often see this challenge, and it requires a deeper dive into aspects like sender reputation, engagement metrics, and subtle content cues that spam filters pick up on. It can be particularly challenging for new sending domains that lack a long history of positive engagement. Let us explore the common culprits and practical solutions.
Beyond authentication: why reputation matters
While having SPF, DKIM, and DMARC configured is fundamental for email deliverability, they are not a silver bullet. These protocols primarily verify that your emails are legitimate and prevent spoofing. Passing these checks means your email is technically authenticated, but it does not guarantee inbox placement, especially with a strict recipient like Gmail. Gmail's spam filters consider a holistic view of your sending practices.
Sender reputation is paramount. Even if your technical setup is perfect, a poor sender reputation can derail your efforts. This reputation is built over time based on factors such as spam complaint rates, bounce rates, recipient engagement (opens, clicks, replies), and whether your IP address or domain appears on any email blocklists (or blacklists). For more information, you can read our guide on understanding your email domain reputation.
A common diagnostic tool is Google Postmaster Tools. This provides insights into your sending reputation with Gmail, including data on spam rates, IP reputation, and domain reputation. I always recommend senders to utilize this tool, as it gives direct feedback from Google's perspective. It helps to identify if you are on any blocklists or facing other issues. Our article on Google Postmaster Tools V2 can assist you in navigating it.
Understanding Gmail's 'Similar to Spam' Classification
When Gmail flags an email as "similar to messages identified as spam in the past," it means that their internal filters (which are constantly learning) have found patterns in your email's content, structure, or sending behavior that resemble past emails identified as spam by users. This is a behavioral flag, not a technical authentication failure.
This can happen even if your emails are welcome to your intended recipients, as Gmail's algorithms learn from a vast dataset. For example, a marketing email may inadvertently use phrases or layouts commonly associated with unwanted bulk email. It is also a reason why transactional emails can sometimes land in spam.
Hidden technical nuances that trip up deliverability
Beyond the major authentication protocols, subtle technical details can significantly impact deliverability. One often-overlooked area is the proper implementation of one-click unsubscribe, particularly the RFC 8058 standard. As of June 1, 2024, Google and Yahoo require bulk senders to support this feature. If it is missing, Gmail may not deliver your emails.
Another technical aspect that often goes unnoticed is the consistency of image and link hosting domains. If your email content (images, tracking links, etc.) is hosted on various domains that do not align with your primary sending domain, it can raise red flags for spam filters. This type of mixed content can appear suspicious, as it is a tactic sometimes used by malicious actors. It is best practice to keep all linked assets on domains that are either your own or reputable Content Delivery Networks (CDNs) consistently used and trusted.
Ensuring your technical setup is consistently aligned and up-to-date with current best practices is crucial. Even if it was not an issue previously, new requirements from major mailbox providers can suddenly affect your deliverability. This can be why emails suddenly go to spam, even when everything seems technically correct.
Inconsistent image and link hosting
Problem: Images are hosted on a variety of third-party domains (e.g., cdn.exponea.com, brxcdn.com) that do not match the sending domain.
Risk: This can appear as suspicious activity to mailbox providers, resembling tactics used in phishing or spam campaigns. It can negatively impact your sender reputation and lead to messages being flagged.
Missing RFC 8058 one-click unsubscribe
Problem: Your email only includes a List-Unsubscribe header, but not the List-Unsubscribe-Post header for one-click unsubscribe.
Risk: Gmail has required RFC 8058 compliance for bulk senders since June 1, 2024. Non-compliance can lead to emails being rejected or sent straight to spam.
Aligned image and link hosting
Solution: Host all images and links on your primary sending domain or a dedicated subdomain that is properly authenticated (e.g., img.yourdomain.com). If using a CDP or ESP, ensure they are properly configured to use your custom tracking domains.
Benefit: Increased trust signals for spam filters, leading to improved inbox placement and a stronger sender identity.
Implementing RFC 8058 one-click unsubscribe
Solution: Add the List-Unsubscribe-Post header in addition to the traditional List-Unsubscribe header. This allows users to unsubscribe with a single click within the email client interface. You can find more details on one-click unsubscribe.
Benefit: Compliance with major mailbox provider requirements and reduced spam complaints, as users can easily opt out.
Maintaining a clean and consistent technical footprint is as important as the initial setup. Even small inconsistencies can add up and lead to deliverability issues over time.
Content quality and recipient engagement
Even with perfect technical setup, the content of your emails can trigger spam filters. Gmail's filters analyze various aspects of your message, including keywords, image-to-text ratio, link density, and overall email design. If your content resembles common spam patterns, it is likely to be flagged, even if your intentions are legitimate.
Engagement metrics are a powerful signal for mailbox providers. If recipients consistently open, click, and reply to your emails, it indicates that your messages are wanted. Conversely, low engagement rates, combined with a high number of deletions without opening or direct spam complaints, will negatively impact your sender reputation. This can lead to your emails being directed to the spam folder, even for engaged recipients.
Content and engagement best practices
Content quality: Avoid excessive use of spam trigger words or phrases commonly associated with spam (e.g., "free money," "act now"). Maintain a healthy image-to-text ratio and ensure your HTML is clean and well-structured. Personalize your content where possible.
Engagement: Encourage interaction by sending relevant, valuable content. Regularly clean your email lists to remove inactive subscribers and avoid sending to old or unengaged addresses. High open rates and click-through rates signal positive engagement.
Feedback loops: Monitor spam complaint rates through tools like Google Postmaster Tools. A high complaint rate (even if small in absolute numbers) is a strong negative signal. Quickly remove users who mark your emails as spam.
A new sending domain will always face an uphill battle initially because it lacks historical data. Even if you are warming it up with legitimate traffic, it takes time to build a strong reputation. Mailbox providers are inherently cautious with new domains to prevent spammers from quickly establishing and burning through them. This is a common reason first emails to new Gmail recipients go to spam.
Understanding sender reputation
Recovering sender reputation takes time and consistent effort. There is no quick fix. You need to consistently send wanted emails and minimize negative signals. How long it takes to recover domain reputationfrom bad to high can vary significantly based on the severity of the issue and your sending volume.
If you are using a new sending domain, even with dedicated IP addresses, your reputation starts from zero. It is essential to warm up the new domain properly, gradually increasing your sending volume to engaged users. This helps mailbox providers like Google learn that your domain sends wanted mail. Skipping this process or sending large volumes too quickly can immediately trigger spam filters, regardless of your authentication setup.
Another factor that impacts domain reputation is the specific ESP (Email Service Provider) or CDP (Customer Data Platform) you use. While an ESP handles the technical sending, a CDP might be responsible for generating the email content and links. If links within your email (e.g., for images or tracking) point to domains associated with a different provider or a shared domain with a poor reputation, it can negatively affect your current sending domain's standing. This is a subtle but critical detail, as it suggests a lack of alignment or potentially suspicious activity.
Factor
Impact on deliverability
How to check
IP reputation
The trust level associated with your sending IP address.
Focus on maintaining a consistently high sender reputation by monitoring engagement and complaint rates regularly.
Ensure all technical configurations, including SPF, DKIM, and DMARC, are correctly set up and aligned.
Implement RFC 8058 one-click unsubscribe to comply with Gmail and Yahoo requirements for bulk senders.
Host all email content, such as images and tracking links, on domains that are consistent with your sending domain or well-known CDNs.
Rigorously clean your email lists to remove inactive subscribers and avoid sending to outdated or unengaged addresses.
Common pitfalls
Assuming that passing SPF, DKIM, and DMARC guarantees inbox delivery, overlooking other crucial factors.
Using a new sending domain without a proper warm-up strategy, leading to immediate flagging by mailbox providers.
Ignoring the impact of content quality, spam trigger words, and image-to-text ratio on spam filter performance.
Failing to monitor feedback loops and rapidly remove users who mark emails as spam, which severely damages sender reputation.
Having inconsistent hosting domains for images and links within your emails, which can appear suspicious to filters.
Expert tips
Regularly check your domain and IP reputation using tools like Google Postmaster Tools for direct insights into how Gmail views your sending.
Prioritize list hygiene. Sending to engaged recipients is far more important than sending to a large but unengaged list.
Always include a clear and easy-to-find unsubscribe link, beyond the required one-click header, to reduce spam complaints.
Test your emails with an email deliverability tester before sending large campaigns to identify potential issues.
Consider segmenting your audience and tailoring content to increase engagement, which positively impacts your sender reputation.
Expert view
Expert from Email Geeks says that if an email is flagged as "similar to messages identified as spam," it typically indicates that the content itself resembles unwanted email in Google's perception.
2024-08-15 - Email Geeks
Expert view
Expert from Email Geeks says that using shared domains for image hosting, such as cdn.exponea.com, can be a contributing factor to emails landing in spam because shared domains can have fluctuating reputations.
2024-08-15 - Email Geeks
Putting it all together for inbox success
When your emails land in spam despite seemingly correct technical configurations, it is often a sign that you need to look beyond the basics. While SPF, DKIM, and DMARC are essential, they are just one part of the complex puzzle of email deliverability.
The key is to adopt a holistic approach, focusing on your sender reputation, ensuring compliance with evolving standards like RFC 8058 one-click unsubscribe, maintaining consistent technical elements, and prioritizing genuine recipient engagement. Continuously monitoring your performance through tools like Google Postmaster Tools and adapting your strategies will be crucial for long-term inbox success.
Addressing these multifaceted aspects will help you overcome the challenge of emails going to spam and ensure your messages reach the inbox where they belong. Sometimes, the problem is not a single issue, but a combination of small factors that accumulate to impact your sending reputation.
Gmail. Gmail's spam filters consider a holistic view of your sending practices.
Google learn that your domain sends wanted mail. Skipping this process or sending large volumes too quickly can immediately trigger spam filters, regardless of your authentication setup.
Yahoo
and Gmail Postmaster Tools, ESP analytics.
