Summary
Even when email accounts share seemingly identical configurations, various factors can lead to one account's emails being marked as spam while the other's reach the inbox. These factors encompass sender reputation (affected by sending history, engagement, and complaints), content variations, list quality and segmentation, tracking domain reputation, IP address reputation within a shared pool, authentication misconfigurations, the absence of feedback loops, ESP's internal scoring, sending volume discrepancies, list hygiene practices, sending authorization record reputation, IP warmup for new IPs, and the inadequacy of relying solely on seed lists for deliverability testing. To mitigate these issues, experts recommend monitoring sender reputation, optimizing email content, verifying authentication settings, implementing feedback loops, maintaining list hygiene, segmenting lists effectively, warming up new IPs, carefully testing deliverability, and analyzing email headers to pinpoint the root causes of spam filtering.
Key findings
- Sender Reputation Dominance: Sender reputation, influenced by engagement, complaints, and history, is a critical determinant of deliverability.
- Content Sensitivity: Even minor variations in content, including keywords and image-to-text ratios, can trigger spam filters.
- List Quality Matters: Variations in list quality, engagement, and how subscribers opted-in greatly affect inbox placement.
- Tracking Domain Impact: The reputation of tracking domains significantly influences email deliverability.
- IP Reputation Variances: Shared IP addresses can have different reputations, affecting deliverability for different accounts.
- Authentication is Essential: Correct SPF, DKIM, and DMARC configurations are vital for avoiding spam filters.
- Feedback Loops are Crucial: Implementing and monitoring feedback loops helps address spam complaints and improve reputation.
- Internal Scoring by ESPs: ESPs may use internal metrics to prioritize or throttle deliverability for certain accounts.
- Sending Volume Impact: Significant discrepancies or sudden increases in sending volume can trigger spam filters.
- List Hygiene is Key: Maintaining clean and up-to-date email lists is essential for avoiding spam placement.
- Authorization Record: The reputation and set-up of sending authorization records matter.
- IP Warming: Failure to correctly warm-up new IP addresses leads to increased chances of spam.
- Seed Lists Limitations: Relying solely on seed lists for deliverability testing can be misleading due to the lack of real user engagement data.
Key considerations
- Proactive Reputation Management: Actively monitor and manage sender reputation using available tools and services.
- Content Optimization: Optimize email content to avoid spam triggers and improve engagement.
- Authentication Verification: Regularly verify and update SPF, DKIM, and DMARC configurations.
- Feedback Loop Implementation: Set up and closely monitor feedback loops to address spam complaints promptly.
- List Hygiene Practices: Implement robust list hygiene practices, including removing invalid addresses and unsubscribes.
- List Segmentation Strategies: Segment email lists based on user engagement and interests to improve targeting.
- IP Warmup Protocols: If using new IP addresses, implement a gradual warmup process to build a positive reputation.
- Deliverability Testing Methodologies: Supplement seed list testing with real user data to accurately assess deliverability.
- Header Analysis Techniques: Analyze email headers to identify specific issues causing spam filtering.
- URL Testing Protocol: Test emails without URLs to determine if tracking links are triggering spam filters.
- Subscribers Opt-In: Ensure that all subscribers have provided explicit and informed consent for email subscriptions.
- Monitor Sending Volume: Avoid rapid increases in email sending volume that could trigger spam filters.
What email marketers say
12 marketer opinions
Even with similar email configurations, multiple factors can cause emails from one account to land in spam while another reaches the inbox. These factors include differences in sender reputation, content variations, list quality, tracking domain reputation, IP address reputation within a shared pool, user engagement levels, ESP's internal scoring, sending volume, and list hygiene practices. Testing URLs, analyzing email headers, monitoring IP address performance, warming up new IPs, and actively managing sender reputation and list quality are all crucial for troubleshooting and maintaining inbox placement.
Key opinions
- Sender Reputation: Differences in sender reputation, even with similar setups, can lead to spam filtering.
- Content Variations: Even slight content variations can trigger spam filters for one account and not the other.
- List Quality: Variations in list quality, such as engagement levels, impact inbox placement.
- Tracking Domains: Different tracking domains can significantly affect deliverability due to associated reputation.
- IP Address Reputation: Shared IP addresses may have varying reputations within the same pool.
- User Engagement: Different levels of user engagement (opens, clicks) influence spam placement.
- ESP Internal Scoring: ESPs might use internal metrics to prioritize deliverability for certain accounts.
- Sending Volume: Significant differences in sending volume can trigger spam filters.
- List Hygiene: Poor list hygiene practices contribute to spam filtering.
- IP Warmup: Failure to warm up a new IP address can lead to emails being marked as spam.
Key considerations
- URL Testing: Test emails without URLs to identify if a URL is triggering spam filters.
- Header Analysis: Compare email headers to understand why one email landed in spam.
- IP Monitoring: Monitor IP addresses sending to spam and inbox to identify problematic IPs.
- Content Scrutiny: Carefully review email content, including subject lines, for potential spam triggers.
- List Segmentation: Segment lists based on engagement and send targeted content.
- Sender Authentication: Review and ensure proper setup of SPF, DKIM and DMARC.
- Feedback Loops: Implement feedback loops to monitor and address spam complaints.
- IP Warmup: If using new IP addresses, warm them up gradually to build a positive reputation.
- Review Sending Volume: Avoid sudden increases in sending volume.
- Ensure List Hygiene: Clean your list to remove invalid emails, unsubscribes, bounces, and spam complaints.
Marketer view
Email marketer from ActiveCampaign Blog shares that one account may have poor list hygiene practices. List hygiene includes, removing invalid email addresses, unsubscribes, bounced emails, and spam complaints.
12 Apr 2024 - ActiveCampaign Blog
Marketer view
Email marketer from Mailchimp Resource Center explains that variations in list quality, even with similar configurations, can lead to different outcomes. One list might have more engaged users than the other, resulting in better inbox placement.
10 Feb 2023 - Mailchimp Resource Center
What the experts say
3 expert opinions
Even with similar configurations, emails from one account may land in spam due to issues related to list segmentation, deliverability testing methodologies, and feedback loop/list hygiene practices. Sending to subscribers who didn't actively opt-in or mismanaging feedback loops and list hygiene can negatively impact sender reputation and increase the likelihood of spam filtering. Relying solely on seed lists for deliverability testing can also provide inaccurate results due to the lack of real user engagement data.
Key opinions
- List Segmentation: Subscribers may not want mail from different accounts, even if they opted-in to one.
- Deliverability Testing: Seed lists are inadequate for fully gauging deliverability due to lack of real user interaction.
- Feedback Loops & List Hygiene: Proper setup of feedback loops and good list hygiene are essential for maintaining sender reputation.
Key considerations
- Opt-in Verification: Ensure subscribers have explicitly opted-in to receive mail from each individual account.
- Real User Testing: Supplement seed list testing with real user data to accurately assess deliverability.
- Implement Feedback Loops: Set up and actively monitor feedback loops to address spam complaints and improve sender reputation.
- Maintain List Hygiene: Regularly clean your email lists to remove invalid addresses, unsubscribes, and bounces.
Expert view
Expert from Word to the Wise highlights the danger of testing deliverability solely with seed lists. Seed lists often lack the engagement history of real users, so an email might perform well on a seed list but poorly with actual subscribers due to factors like lack of prior interaction and differing spam filter responses.
13 Feb 2025 - Word to the Wise
Expert view
Expert from Email Geeks suggests considering whether subscribers are actively subscribing to mail from one account and then being added to a different list. If subscribers don't expect mail from the second list and interact with it negatively, it can negatively impact the email's reputation.
19 Oct 2022 - Email Geeks
What the documentation says
5 technical articles
Despite similar configurations, documentation from Google, Microsoft, RFC Editor, SparkPost, and AWS indicates several technical and reputation-based factors can cause one account's emails to land in spam while another's reach the inbox. These factors include sender reputation (influenced by past sending behavior and engagement metrics), content filtering (triggered by subtle differences in email content or structure), authentication misconfigurations (in SPF, DKIM, or DMARC), the absence of feedback loops, and the reputation of sending authorization records.
Key findings
- Sender Reputation: A lower sender reputation, due to past behavior and engagement, leads to spam filtering.
- Content Filtering: Subtle content differences, like keywords or image-to-text ratio, trigger spam filters.
- Authentication Issues: Misconfigurations in SPF, DKIM, or DMARC can flag an account as spam.
- Feedback Loops: Lack of feedback loops prevents learning from spam complaints and degrades reputation.
- Authorization Records: A weaker reputation of sending authorization records can lead to spam placement.
Key considerations
- Monitor Sender Reputation: Regularly monitor sender reputation using tools like Google Postmaster Tools.
- Optimize Content: Optimize email content to avoid triggering spam filters, paying attention to keywords and image-to-text ratios.
- Verify Authentication: Thoroughly verify SPF, DKIM, and DMARC configurations for both accounts.
- Implement Feedback Loops: Set up and actively monitor feedback loops to handle spam complaints.
- Review Sending Authorization Records: Ensure that sending authorization records are correctly configured and maintained.
Technical article
Documentation from Microsoft 365 documentation states that content filtering is a primary reason. Slight differences in email content, even if seemingly negligible, can cause different outcomes. For example, using certain keywords or having a different image-to-text ratio in one account can trigger spam filters.
16 Jan 2023 - Microsoft 365 documentation
Technical article
Documentation from Google Postmaster Tools Help explains that sender reputation is a crucial factor. Even with similar configurations, one account might have a lower reputation due to past sending behavior, complaint rates, or engagement metrics, leading to spam filtering.
7 Jun 2022 - Google Postmaster Tools Help
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