Why are Gmail emails deferred or undelivered only to Italian subscribers after switching ESPs and subdomains?

Key findings

• Geographic anomaly: The deliverability issues are exclusively affecting Italian Gmail subscribers, while emails to other countries are performing well, suggesting a localized factor.
• New infrastructure: The problem emerged after switching ESPs and transitioning from a corporate domain to a new subdomain, introducing a new sending identity.
• Early warmup: The warmup period for the new setup has only been two days, which is generally insufficient to establish full sender reputation.
• Reputation metrics: The domain is not blocklisted, and the IPs show a high SenderScore, yet emails are not reaching the inbox.
• Delivery discrepancy: Emails are reported as 100% delivered by the ESP, but opens are very low, and test emails are not visible in any recipient folders, indicating a likely spam folder placement or silent discarding.

Key considerations

• Warmup duration: The early stage of warmup is highly volatile, and initial poor performance is common. It often requires more time to stabilize.
• Missing data: The absence of bounce messages or data from Google Postmaster Tools makes precise diagnosis difficult.
• List quality: Investigate the Italian subscriber acquisition method and list hygiene, especially if the previous ESP was suppressing certain addresses that are now active again.
• Localized filtering: Consider if specific content, language encoding, or local ISP policies for Italy could be impacting delivery. For more details on deferred emails, refer to Mailercloud's guide to Gmail rejection and deferral messages.

Key opinions

• Immediate impact: Marketers quickly notice significant drops in email performance, such as very low open rates despite high reported delivery rates by the new ESP.
• Geographic focus: The observation that only specific regional segments, like Italian subscribers, are affected leads to initial thoughts about localized filtering or audience-specific issues.
• Previous performance contrast: There's often confusion as the same list and content delivered successfully with the previous ESP, making the current issues perplexing.
• Test visibility: When test emails don't appear in the inbox or spam folder, it raises concerns about silent filtering or deep-level blocklisting.

Key considerations

• True inbox placement: Marketers need to verify if emails are truly landing in the inbox, or if they are being redirected to spam/promotional tabs, even if the ESP reports 100% delivery. This highlights why emails go to spam.
• Interpreting delivery stats: Understanding what deferred or undelivered statuses truly mean from the new ESP is vital. Sometimes, a deferred email is a temporary delay, not a permanent block.
• Segmentation details: Reviewing how Italian subscribers were acquired and if their engagement patterns differ significantly from other segments is important.
• Warmup patience: Recognizing that early warmup data can be misleading and that consistency is key for reputation building.

Key opinions

• Warmup period: A two-day warmup is considered very short, and initial deliverability fluctuations, including deferrals or undelivered messages, are expected and normal behavior for a new sending domain.
• Diagnostic data: Bounce messages and non-delivery reports (NDRs) are crucial. Without them, it is impossible to understand the precise reason for delivery issues from Gmail.
• Patience advised: Experts strongly recommend waiting at least 4-5 days into the warmup before actively troubleshooting, as early issues often resolve themselves.
• List source scrutiny: Potential problems with the subscription form used for the Italian audience or a failure to migrate suppressed addresses from the old ESP are common culprits for sudden deliverability drops.
• Technical nuances: If unique content or language encoding is used for Italian emails, it might be worth checking for any technical misconfigurations that could cause filtering.

Key considerations

• Statistical insignificance: Deliverability is a game of probability and statistics; a very small sample size of emails (e.g., 8 test emails) is insufficient for drawing reliable conclusions, as discussed in articles on sudden deliverability drops.
• Google postmaster tools: While not immediately available, monitoring this tool is critical once data populates for understanding Gmail's specific view of sender reputation.
• Pre-existing suppressions: It's vital to confirm if the previous ESP was suppressing a significant number of addresses, and if those suppressions were correctly carried over to the new infrastructure. For more on deferrals, refer to Campaign Refinery's guide.
• Domain reputation building: New subdomains and IPs need time to build trust. Consistent, good sending practices are far more effective than immediate troubleshooting during the very early days, as detailed in discussions around domain reputation recovery.

Key findings

• Warmup necessity: Documentation from major mailbox providers consistently recommends a structured, gradual increase in sending volume for new IPs and domains to build a positive sender reputation and avoid early filtering.
• Reputation building: Sender reputation is primarily established through consistent, engaged sending, low complaint rates, and strict adherence to email best practices. This includes maintaining clean lists and sending relevant content.
• Authentication standards: Proper configuration of email authentication protocols like SPF, DKIM, and DMARC is fundamental for proving sender legitimacy and preventing spoofing, which directly impacts deliverability.
• Bounce insights: SMTP bounce codes and detailed extended bounce messages provide specific, actionable reasons for delivery failures, differentiating between temporary deferrals and permanent rejections.
• Diagnostic tools: Tools like Google Postmaster Tools are recommended for monitoring Gmail-specific metrics, including spam rate, IP reputation, and DMARC errors.

Key considerations

• Gradual ramp-up: Adhering to a carefully planned volume increase during warmup is paramount. Rushing this phase can lead to prolonged deliverability issues and reputation damage.
• Monitoring feedback: Relying on ESP-provided bounce logs, DMARC reports, and official postmaster tools is crucial for understanding why emails are not reaching the inbox, beyond simple delivery counts.
• Content relevance: Even with perfect technical setup, content quality and recipient engagement significantly influence inbox placement. Generic or irrelevant content can still land in spam.
• Regional specifics: While core principles are universal, some documentation acknowledges that specific regions or ISPs might have unique content filtering preferences or localized blocklists (blacklists) due to local spam trends. For further reading on deferred emails, refer to this Mailercloud article.