Why are transactional emails with passing SPF, DKIM, and DMARC landing in spam?

Key findings

• Authentication baseline: Authentication protocols (SPF, DKIM, DMARC) verify sender identity but do not ensure inbox placement alone. They are foundational, but not a guarantee. Mailgun emphasizes this point, noting that authentication is a prerequisite.
• Reputation matters: Even with perfect authentication, a poor sender reputation (for your IP or domain) can cause emails to be flagged as spam. This reputation is built over time based on sending history, volume, and recipient interactions.
• Content and audience issues: The content of the email itself (spammy keywords, poor formatting, broken links) or issues with the recipient list (high bounces, spam complaints) are often primary reasons for inboxing issues when authentication passes.
• Development testing impact: Automated or high-volume development testing to unengaged internal addresses can negatively affect domain reputation and spam scores. Mailbox providers interpret a lack of engagement as a negative signal, regardless of the email's purpose. Learn more about troubleshooting emails landing in spam despite passing DMARC, SPF, and DKIM.
• Engagement signals: Mailbox providers prioritize user engagement. If transactional emails are sent to unmonitored mailboxes (e.g., test accounts) or if recipients rarely open, click, or reply, it can signal low sender quality.

Key considerations

• Isolate testing: Use a dedicated subdomain for development and testing environments to prevent deliverability issues from affecting your main sending domain. This is crucial for maintaining a healthy sender reputation.
• Monitor content: Even simple transactional emails can contain elements that trigger spam filters. Review content for any hidden links, unusual formatting, or words commonly associated with spam.
• Sender reputation review: Actively monitor your sender reputation using tools like Google Postmaster Tools or other deliverability platforms. Address any reported issues promptly. You can refer to our guide on why emails go to spam.
• Recipient engagement: Ensure that the recipients of your transactional emails are genuinely expecting them and have a history of engaging with your mail. High unengagement can degrade reputation.

Key opinions

• Beyond authentication: Many marketers find that passing SPF, DKIM, and DMARC is just the entry ticket; the real work of deliverability involves many other factors. As MessageFlow states, incorrect configuration beyond basic authentication can still cause issues.
• Content and audience issues are primary: Marketers frequently point to content-related spam triggers or issues with the recipient audience (e.g., low engagement, spam complaints) as the main culprits when authentication is correctly set up.
• Dev testing risks: Automated development testing, especially when not properly isolated, is seen as a significant risk that can inadvertently damage a sending domain's reputation due to lack of real engagement.
• The 'no-reply' debate: While some argue filters don't explicitly penalize 'no-reply' addresses, many marketers advise against them due to the negative user experience and the missed opportunity for engagement feedback.
• Overall context matters: Mailbox providers assess the entire sending context, including sender behavior over time, the types of emails sent, and how recipients interact with them. This is why transactional emails can still go to spam.

Key considerations

• Content audit: Regularly audit your email content for elements that might trigger spam filters, even for simple transactional messages. This includes analyzing text, links, and HTML structure.
• Dedicated testing environments: Implement a separate subdomain or IP for all development and testing to prevent test emails from impacting the reputation of your primary sending infrastructure. This helps in understanding your email domain reputation.
• Monitor engagement: Actively track engagement metrics for your transactional emails, such as open rates and click-through rates. Low engagement can be a red flag for mailbox providers.
• Use monitoring tools: Leverage deliverability monitoring tools to gain insights into how your emails are being perceived by different ISPs and identify potential issues before they escalate.

Key opinions

• Deliverability is earned: Authentication simply allows you to receive the deliverability you deserve. It does not grant a free pass to the inbox, as reputation and behavior are key.
• Beyond technical passes: If authentication is passing, the issue most likely lies with content, audience engagement, or an underlying reputation problem. It's not always a technical authentication failure.
• Automated testing risks: Automated development testing can significantly harm sender reputation if the test emails are sent to unengaged addresses or in large volumes, as ISPs track engagement metrics. Learn more about what to do when emails are blocked.
• Content filtering: Even minimal or plain text content (like a 'test' email) can be filtered by Gmail, indicating that content analysis is a critical component of their spam filtering algorithms.
• rDNS and IP reputation: For development systems, ensuring proper rDNS (reverse DNS) setup and avoiding random IPs, especially those in cloud provider spaces (like AWS), is important for maintaining trust.

Key considerations

• Subdomain isolation: Always conduct development and testing from a separate subdomain to protect your primary domain's reputation from potential negative impacts. This prevents accidental mass sends from damaging your brand.
• Comprehensive testing: When troubleshooting, test the actual email content and template. If basic authentication passes, the issue is often in the message's presentation or how it's perceived by filters. You can use Google Postmaster Tools to improve reputation.
• Recipient behavior analysis: Examine how recipients (even internal ones) interact with your test emails. Low engagement signals can still harm reputation even if unintended for production.
• Analyze ISP feedback: When emails land in spam, analyze any available feedback from the mailbox provider (e.g., through Postmaster Tools) to pinpoint the exact reason, rather than solely relying on authentication passes.

Key findings

• Authentication's role: SPF, DKIM, and DMARC primarily serve to verify the authenticity of a sender and protect against spoofing and phishing attempts, not to guarantee inbox delivery.
• Part of broader strategy: DMARC, while powerful, is only one component of a comprehensive anti-spam strategy employed by receiving mail servers. Mailbox providers use many other signals.
• Reputation and content: Documentation often highlights sender reputation (based on complaints, bounces, engagement) and email content quality as crucial elements alongside authentication for inbox placement.
• DMARC policy actions: DMARC allows senders to instruct receiving servers on how to handle emails that fail SPF or DKIM checks, offering policies like 'none', 'quarantine', or 'reject'. More about DMARC tags and their meanings.
• ISP filtering: ISPs continuously refine their algorithms to identify and filter spam, relying on a multitude of data points beyond simple authentication passes to protect user inboxes. Read our ultimate guide to Google Postmaster Tools.

Key considerations

• Review bulk sender guidelines: Adhere to the specific bulk sender guidelines published by major mailbox providers like Gmail and Yahoo, which outline expectations for sender behavior and technical setup beyond authentication.
• Monitor DMARC reports: Regularly analyze DMARC reports to gain insights into how your emails are being authenticated and handled by receiving servers, identifying potential issues even when authentication passes.
• Content quality: Ensure your email content is clear, concise, and avoids characteristics commonly found in spam (e.g., excessive capitalization, suspicious links, poor grammar).
• Feedback loops: Enroll in ISP feedback loop programs to receive notifications about user spam complaints, which are critical signals for reputation management.