Why are transactional emails with passing SPF, DKIM, and DMARC landing in spam?
Matthew Whittaker
Co-founder & CTO, Suped
Published 15 Jul 2025
Updated 18 Aug 2025
7 min read
It can be frustrating when you diligently set up all your email authentication protocols—Sender Policy Framework (SPF), DomainKeys Identified Mail (DKIM), and Domain-based Message Authentication, Reporting, and Conformance (DMARC)—only to find your transactional emails still landing in the spam folder. I've heard this question many times, and it highlights a common misconception: passing authentication, while crucial, doesn't guarantee inbox placement. It simply means you've proven you are who you say you are.
Authentication is a fundamental layer of trust in the email ecosystem, helping mailbox providers distinguish legitimate senders from spammers. However, modern spam filters (or blocklist algorithms) employ a much broader set of criteria to evaluate incoming mail. These criteria often weigh heavily on sender reputation, content quality, and recipient engagement.
So, if your SPF, DKIM, and DMARC records are all correctly configured and passing, and yet your critical transactional emails are still being flagged as spam, it means the issue lies elsewhere. I'll walk you through the primary reasons this happens and what you can do to fix it.
Even with perfect authentication, your sender reputation is paramount. Mailbox providers like Gmail (Microsoft Outlook) and Yahoo maintain sophisticated internal scoring systems for every sending IP and domain. A low reputation score can lead to emails being sent to spam, regardless of authentication passes. This score is influenced by a multitude of factors, building over time with every email sent.
Key reputation signals include recipient engagement (opens, clicks, replies), spam complaints, bounces, and whether your IP or domain appears on public or private blocklists (also known as blacklists). Even a small increase in spam complaints or a high bounce rate can severely impact your sender reputation, pushing otherwise legitimate emails into the spam folder. I find that many senders only focus on authentication, missing the broader picture of their reputation.
For instance, if your domain or IP is listed on a major email blacklist (or blocklist), it signifies to receiving servers that you may be a source of unwanted mail. This can lead to emails being blocked or routed directly to spam, even if authentication passes. Regular blocklist monitoring is essential for identifying and addressing these issues promptly.
The impact of sender reputation
Authentication simply verifies who sent the email, not the quality or desirability of the mail. A strong sender reputation is built over time through consistent good sending practices, positive recipient engagement, and a low rate of negative feedback like spam complaints or bounces.
Mailbox providers maintain internal scoring systems that assess your sending behavior, and this score heavily influences inbox placement. Passing authentication is a baseline, but without a good reputation, your emails are still at high risk of being filtered.
Content and engagement are crucial
Even for transactional emails, content and how recipients interact with it play a significant role. Filters analyze email content for spammy keywords, excessive use of exclamation points, all caps, or suspicious links. Poorly formatted HTML, a high image-to-text ratio, or broken links can also raise red flags.
Engagement signals are critical. If recipients frequently delete your emails without opening them, move them to spam, or simply ignore them, this negative feedback tells mailbox providers that your emails are not desired. This is particularly true for transactional emails, which usually have very high expected engagement rates due to their immediate relevance to the user.
While using a 'no-reply' email address might seem convenient for transactional messages, it can indirectly affect your deliverability. It discourages replies and fosters a one-way communication channel, which can subtly contribute to lower engagement rates over time. Although it doesn't directly trigger spam filters, the lack of an easy reply option can make some recipients more likely to mark an email as spam if it's not immediately clear or expected.
Good content practices
Clear and concise: Ensure your message is easy to understand and directly addresses the purpose of the transactional email.
Relevant subject lines: Use descriptive subject lines that accurately reflect the email's content.
Personalization: Personalize emails where appropriate, even for transactional messages, to enhance relevance.
High engagement: Encourage positive interactions like opens and clicks by delivering expected, valuable information.
Bad content practices
Spammy triggers: Avoid words or phrases commonly associated with spam, even in transactional contexts.
Poor formatting: Overuse of images, broken HTML, or too many fonts can look suspicious to filters.
'No-reply' addresses: While not a direct filter trigger, they can discourage replies and positive engagement.
Low engagement: Consistent low open rates or high deletion rates signal a lack of relevance.
Audience quality and list hygiene
The quality of your recipient list directly impacts your deliverability. Sending to a list with a high percentage of invalid, inactive, or purchased email addresses will quickly damage your reputation. Mailbox providers monitor how many emails sent from your domain bounce or are sent to users who rarely open your mail. A high bounce rate is a strong negative signal, even if authentication passes.
Spam traps are a critical concern. These are email addresses specifically set up by internet service providers (ISPs) and anti-spam organizations to identify senders of unsolicited email. Hitting a spam trap, even once, can severely damage your sender reputation and lead to immediate blacklisting (or blocklisting) of your IP or domain. You can learn more about how they work in our guide to spam traps.
Regular list hygiene is non-negotiable. This means removing hard bounces, inactive subscribers, and regularly verifying email addresses. For transactional emails, ensuring that you're only sending to users who have explicitly opted in or have a recent, legitimate interaction with your service is key to maintaining a clean and engaged audience.
Warning about spam traps
A common reason for good emails hitting spam is inadvertently sending to spam traps. These addresses are designed to catch senders with poor list management. Even a single hit can severely damage your reputation, leading to blocklisting and subsequent spam folder delivery for all your emails.
Always ensure your lists are opt-in, regularly cleaned, and never purchased. Validate email addresses at the point of collection to minimize the risk of hitting these traps and facing deliverability issues, especially for transactional emails going to spam.
Technical considerations and infrastructure
While your SPF, DKIM, and DMARC might show a pass, subtle technical issues or misconfigurations can still impact deliverability. For instance, SPF records can have DNS lookup limits. If you include too many mechanisms, your SPF record might technically pass but cause issues for some receivers due to timeouts. Similarly, DMARC requires alignment between the 'From' domain and the SPF/DKIM domains, and even if authentication passes, an alignment failure can lead to spam placement.
Another often overlooked technical aspect is Reverse DNS (rDNS) for your sending IPs. rDNS (or PTR record) maps an IP address back to a hostname. Many mailbox providers perform rDNS lookups, and if your sending IP doesn't have a properly configured rDNS record that matches your sending domain, it can negatively impact your deliverability. This is especially relevant if you are sending from your own infrastructure or a cloud provider's IP space.
Finally, how your development and testing environments are set up can inadvertently affect your production domain's reputation. If developers are sending numerous test emails from your main domain, especially to unmonitored or invalid addresses, this can create negative engagement signals that harm your overall sender reputation. It's often best practice to use a dedicated subdomain, like dev.yourdomain.com, for all development and testing activities to isolate any potential negative impacts from your primary sending domain.
Example: Check an IP's rDNS record (PTR)bash
dig -x 203.0.113.42 +short
Factor
Impact on deliverability
What to check
SPF DNS lookup limit (10)
Emails may fail SPF validation if too many mechanisms require DNS lookups, even if the record appears valid.
Ensure your SPF record doesn't exceed 10 DNS lookups.
DMARC alignment
Emails can fail DMARC even if SPF/DKIM pass if the 'From' domain doesn't align with the authenticated domains.
Verify your DMARC aggregate reports using DMARC monitoring to check alignment issues.
Reverse DNS (PTR) record
Many ISPs check for valid rDNS. Missing or mismatched records can lead to emails being rejected or spammed.
Ensure your sending IP's rDNS record points to your sending domain.
Views from the trenches
Best practices
Segment your email lists carefully and ensure you are only sending to engaged recipients.
Regularly clean your email lists to remove inactive addresses, bounces, and potential spam traps.
Maintain consistent sending volumes and patterns to build a stable sender reputation.
Use a dedicated subdomain for development and testing environments to isolate deliverability risks from your main domain.
Personalize transactional emails where possible to increase relevance and engagement, even simple ones.
Common pitfalls
Relying solely on SPF, DKIM, and DMARC passes as a guarantee for inbox delivery.
Ignoring engagement metrics like open rates, click rates, and spam complaint rates for transactional emails.
Sending to old, unverified, or purchased email lists that may contain spam traps.
Using generic 'no-reply' email addresses which can subtly discourage engagement.
Failing to configure reverse DNS (PTR records) for dedicated sending IPs.
Expert tips
"Authentication gives you the deliverability you deserve, but it's not a get out of jail free card. You need to look at your mail types, IP/domain infrastructure, mailing frequency, and list hygiene," an expert from Email Geeks says.
"Development testing can cause delivery issues, especially if it's automated and sends too many emails to unengaged addresses," an expert from Email Geeks warns.
"If emails are landing in spam and authentication is passing, the problem is usually either a content issue or an audience issue. For testing content, it's very often content related," an expert from Email Geeks explains.
"Make sure your reverse DNS is set up correctly and your sending IP isn't from a generic cloud provider space that lacks proper reputation," an expert from Email Geeks advises.
"Make your developers test from a dedicated subdomain so they don't accidentally ruin your main domain's reputation with large test sends," a marketer from Email Geeks emphasizes.
Marketer view
A marketer from Email Geeks says that authentication is a crucial baseline, but inbox placement depends on many other factors like mail type, infrastructure, sending frequency, and list hygiene.
2025-01-28 - Email Geeks
Marketer view
A marketer from Email Geeks points out that dev testing, especially if automated, can easily lead to deliverability issues.
2025-01-28 - Email Geeks
Achieving consistent inbox placement
While SPF, DKIM, and DMARC are the bedrock of email authentication and essential for deliverability, they are only one piece of a much larger puzzle. Consistent inbox placement for transactional emails, particularly at major providers like Gmail, relies on a holistic approach that prioritizes sender reputation, content quality, and recipient engagement. By paying close attention to these additional factors and employing robust monitoring strategies, you can significantly improve your chances of consistently landing in the inbox.
Gmail
(Microsoft Outlook)
and Yahoo maintain sophisticated internal scoring systems for every sending IP and domain. A low reputation score can lead to emails being sent to spam, regardless of authentication passes. This score is influenced by a multitude of factors, building over time with every email sent.
