Why are emails from one account going to spam while emails from another account are not, despite having similar configurations?

Key findings

• Tracking link influence: While suspected, simply changing a tracking link subdomain for the problematic account (e.g., account1.tool to newaccount1.tool) did not resolve the spam issue, suggesting deeper underlying causes than just the immediate URL.
• Consistent behavior: Across multiple tests with the same list, content, and sender details, account-1 consistently went to spam while account-2 consistently reached the inbox.
• Shared infrastructure: Both accounts operate from the same email service provider (ESP), utilizing identical SPF, DKIM, domain, and even the same pool of three IP addresses, all reported with good reputation scores.
• Generic spam flagging: Gmail's spam notification for the problematic account stated, "It is similar to messages that were identified as spam in the past," indicating a historical pattern or content-based filtering.
• Sender reputation divergence: Despite similar technical configurations, the two accounts likely have distinct sender reputations built on recipient interactions over time, leading to different inbox placements.

Key considerations

• Recipient expectation: A critical factor is whether recipients explicitly opted into receiving emails from both accounts. Even if the list is the same, if users don't expect mail from one specific sender identity, it can trigger spam complaints or low engagement, hurting its reputation.
• Subtle differences: Even with identical SPF and DKIM, there might be other subtle, unexamined differences between the two accounts, such as specific headers, sending patterns, or previous recipient interactions that are influencing deliverability. Examining detailed email headers could reveal these.
• Content and domain reputation: The content itself, or the reputation associated with the specific tracking domain (even if changed to a new one within the same sub-domain structure), could be affecting performance. If the new tracking domain is still perceived as related to the problematic one, it might inherit its poor reputation.
• IP address utilization: Although both accounts use the same IP pool, it is important to verify which specific IP from the pool is being used for each problematic email. A single IP within a pool could be experiencing temporary reputation issues even if the overall pool is generally good.

Key opinions

• URL impact: Marketers frequently suspect tracking links or embedded URLs as a primary cause for spam filtering, especially if one account's links have a history of issues.
• Recipient behavior: Many believe that how recipients interact with emails, such as opening, clicking, or marking as spam, creates a specific reputation for that sending identity, regardless of shared IPs.
• Subdomain reputation: The reputation of a tracking subdomain, even if part of a larger ESP domain, can become independently tarnished, affecting only emails routed through it.
• List segmentation: Sometimes the same list behaves differently if it was originally acquired or segmented for one account versus another, leading to varied engagement.
• IP cycling: Even with multiple IPs, marketers acknowledge that a specific problematic IP in the rotation can disproportionately affect deliverability for the account it serves at a given time.

Key considerations

• Test without URLs: A crucial first step is to remove all URLs from the problematic email and send a test to determine if the issue is indeed link-related.
• Compare headers: Marketers should meticulously compare email headers from both successful and failed deliveries to pinpoint any hidden disparities, especially concerning infrastructure and authentication details. This can offer clues as to why emails are landing in spam.
• Check domain reputation: Utilize tools like Google Postmaster Tools (GPT) to assess the domain reputation of both the sending and tracking domains. Even if the sender domain is shared, subdomains can have unique reputations.
• User opt-in: Confirm that all recipients explicitly opted into receiving emails from the problematic account's specific identity. A lack of this can increase spam complaints, leading to the domain or IP being added to a blacklist or blocklist.

Key opinions

• Troubleshooting difficulty: Experts find it difficult to troubleshoot without full visibility into the exact email samples, IP addresses, and domain configurations of both accounts.
• Recipient expectation: A key tenet is that users must actively opt-in and expect mail from a specific sender. If they do not, even if the list is technically the same, negative recipient actions can accrue.
• Subtle domain reputation: Even with the same root domain, different subdomains or tracking links can develop independent reputations based on their specific usage and associated user feedback.
• Engagement feedback: Inbox providers like Gmail use sophisticated algorithms that learn from user engagement. If one account has historically lower engagement or higher complaint rates, it will be treated differently.
• Holistic view: Experts stress that deliverability is a multi-faceted challenge involving not just technical setup (SPF, DKIM, DMARC), but also content quality, list hygiene, and recipient interaction.

Key considerations

• Analyze sending patterns: Look closely at the volume, frequency, and composition of emails sent by each account, as even slight variations can impact how inbox providers perceive them. This might shed light on why emails go to spam.
• Review historical data: Delve into the history of account-1. Has it had periods of higher complaints, bounces, or unsubscription rates? Past performance heavily influences current reputation.
• Dedicated vs. shared IPs: Even within a shared IP pool, one account might be more frequently routed through an IP that has transient issues, or a particular IP's reputation could be subtly different, even if overall scores are good.
• Content scanning: Consider if there are subtle content differences over time, or if one account's content has ever triggered specific spam filter rules (e.g., specific keywords, image-to-text ratio, or HTML structure issues).

Key findings

• Authentication importance: Properly configured SPF and DKIM are fundamental, but their presence alone does not guarantee inbox delivery if other factors are poor.
• Sender reputation: Documentation across platforms emphasizes that sender reputation, built on consistent positive engagement and low complaint rates, is a critical factor for avoiding the spam folder.
• Engagement rates: Low open and click-through rates, coupled with high unsubscription or spam complaint rates, signal to inbox providers that recipients do not value the mail, leading to spam placement.
• Content quality: Poor email design, excessive images, broken links, or 'spammy' keywords can trigger filters, regardless of sender reputation. Following HTML best practices is important.
• List hygiene: Sending to outdated lists or those containing spam traps can severely damage sender reputation and result in emails landing in spam.

Key considerations

• Verify DNS records: Ensure all DNS records, including PTR records for your IPs and SPF for your domains, are correctly configured and propagated. Missing or incorrect records can lead to emails being flagged, as highlighted by Web Applications Stack Exchange.
• Monitor engagement metrics: Continuously track open rates, click rates, and spam complaints for each distinct sending account. A decline in positive engagement for one account will inevitably affect its deliverability.
• Audit content: Regularly audit email content for potential spam triggers, including suspicious keywords, excessive links, or inconsistent formatting. Adhere to CAN-SPAM compliance and other relevant regulations.
• Review subscriber source: Confirm that the subscribers on the problematic account's list were acquired through legitimate, explicit opt-in methods, and that their expectations align with the emails they receive.