Summary
Migrating email sending to a new subdomain can be a complex process, particularly when dealing with large volumes and existing reputation challenges. The scenario described involves moving a high daily volume of emails, approximately 25 million, from a primary domain to a subdomain, with a phased warm-up strategy across multiple Message Transfer Agents (MTAs). A critical issue has arisen where the reputation at Gmail is dropping, specifically on an older MTA that is now exclusively handling low-engagement campaigns (categorized as 'A' and 'SS'). These segments, despite their low engagement, are deemed financially important, complicating the standard advice to simply cease sending to them.Common deliverability issues during new IP and subdomain warmup often arise from an imbalance in the quality of traffic sent through specific parts of the sending infrastructure. The proposed solution involves a full redistribution of all campaign types across the MTAs to balance the load and engagement quality.
Key findings
- Reputation decline: The Gmail reputation drop is concentrated on MTA 1, which now solely handles the lowest engagement campaigns ('A' and 'SS').
- Traffic imbalance: MTA 1 carries a disproportionately high volume of email (over 15 million messages) compared to the newly warmed MTAs.
- Engagement versus revenue: The 'A' and 'SS' segments, while perceived as revenue-generating, are characterized by low engagement metrics, indicating potential underlying data quality problems.
- Subdomain vulnerability: Ongoing reputation issues on the primary domain's MTA 1 could negatively impact the reputation of the new subdomain.
Key considerations
- Data quality priority: The core problem likely lies in data quality and marketing strategy rather than just technical MTA configuration.
- Strategic redistribution: Distributing all campaign types, including low engagement ones, across all MTAs is a more balanced approach for reputation management.
- List hygiene: Aggressive cleaning of disengaged and inactive subscribers is crucial to improving overall sender reputation and resolving a low Gmail domain reputation.
- Hourly traffic density: Beyond daily volume, managing the concentration of traffic within specific hours is important to avoid spikes that can trigger filters, as highlighted by experts on fixing bad IP reputation.
What email marketers say
Email marketers often face the dilemma of balancing perceived short-term revenue from broad mailing lists with the long-term health of their sender reputation. When migrating to new infrastructure, there's a strong consensus that isolating low-engagement segments on specific MTAs can quickly undermine deliverability efforts. Instead, a more integrated approach, where problematic segments are blended with higher-performing ones during warm-up, is recommended. The focus shifts from merely moving volume to ensuring the quality and distribution of data supports a positive sending signal. Maintaining a strong Gmail sender reputation is paramount, as even minor issues can propagate.
Key opinions
- Segment isolation risk: Isolating low-engagement segments ('A' and 'SS') on a single MTA during migration is a flawed strategy that can significantly harm the parent domain's reputation.
- Blended warm-up: A better warm-up approach involves distributing a percentage of low-engagement campaigns alongside higher-engagement ones from the outset, rather than moving all the problematic data at the end.
- Holistic deliverability: Deliverability issues are often symptoms of deeper data, strategy, and marketing problems, not just technical sending. Even factors like email design can influence overall deliverability rates through engagement.
- Subdomain reputation: Even a small percentage of problematic volume on a subdomain can have a disproportionate negative impact on the overall domain's reputation if it's not managed carefully.
Key considerations
- Strategic list management: Ensure that your list segmentation and distribution strategy across MTAs supports a positive sending signal, especially during migration.
- Proactive engagement: Actively work to re-engage or remove unengaged subscribers to prevent them from damaging your sender reputation.
- Reputation alignment: Understand that the health of your primary domain's reputation will directly influence the reputation of your new subdomain.
- Improving deliverability: Implement strategies to improve deliverability and open rates, particularly when dealing with a bad domain reputation and unengaged users.
Marketer view
Email marketer from Email Geeks suggests that the current warm-up strategy, which leaves the lowest engagement campaigns on MTA 1 for last, is likely contributing to the reputation drop. It would have been more effective to integrate a percentage of these less engaged campaigns with the higher-engagement ones from the beginning of the migration. This gradual blending ensures a more balanced signal to ISPs and prevents a sudden negative shift.
Marketer view
An email marketing strategist from LinkedIn advises that isolating low engagement segments on a single sending IP or MTA during a migration is a common pitfall. This concentration can disproportionately impact the overall sender reputation. A diversified sending strategy from the start, distributing all types of traffic, typically yields better long-term deliverability outcomes.
What the experts say
Deliverability experts consistently point out that what often appears as a technical deliverability issue is, at its root, a problem of data quality, strategy, and marketing approach. They challenge the notion that large, disengaged lists are truly revenue-generating assets, arguing they instead represent significant cost and risk. Key to their advice is an aggressive stance on list hygiene, identifying and removing non-responsive contacts. Experts also stress that recovering domain reputation is a long-term commitment that prioritizes sending to engaged audiences. Furthermore, they highlight the nuances of sending volume and patterns, such as hourly traffic density, which are critical for maintaining a positive sender profile with ISPs.
Key opinions
- Root cause: Many deliverability problems are fundamentally issues of data quality, marketing strategy, and audience engagement, rather than just technical sending configurations.
- Inactive list fallacy: Large segments of inactive or low-engagement contacts, like 'A' and 'SS', are often a net negative, incurring costs and risks without significant revenue generation.
- Aggressive hygiene: Proactive and regular cleaning of email lists, identifying and removing contacts who have not engaged for an extended period, is essential. This helps to recover Gmail email deliverability and sender reputation.
- Active vs. inactive ratio: A key indicator of sender health is ensuring that the volume of emails sent to active subscribers is not less than the volume sent to inactive ones.
- Hourly density: Beyond daily email volume, the hourly traffic density (sending large volumes in very short bursts) significantly impacts sender reputation.
Key considerations
- Re-engagement strategy: Before removing subscribers, consider a targeted re-engagement strategy for those who were previously active but have gone dormant.
- MTA queue management: Be aware that MTA retry settings apply to the entire queue, meaning bad records can halt or pause sending for good data, potentially leading to bounces for otherwise valid emails.
- Differentiated sending: Not all 'old' or inactive data is the same; apply different sending rules or re-engagement tactics based on the specific history of the contact.
- Strategic foundation: Understand that deliverability is a consequence of a sound email strategy, and merely adjusting MTA settings will not solve underlying data quality issues, as emphasized by leading deliverability resources.
Expert view
Deliverability expert from Email Geeks states that, from a brief look at response rates, the issue is not purely a deliverability problem but rather a symptom of deeper data, strategy, and marketing challenges. This perspective emphasizes that technical sending issues often arise because of fundamental flaws in how email lists are managed and how campaigns are designed. Addressing these foundational issues is critical for long-term email program health.
Expert view
Deliverability expert from Spam Resource stresses that continuously mailing unengaged recipients sends negative signals to ISPs, leading to a decline in sender reputation. This gradual erosion of trust ultimately impacts even highly engaged segments, making it harder for all emails to reach the inbox. It underscores the importance of list hygiene as a preventative measure for maintaining deliverability.
What the documentation says
Official documentation from major mailbox providers like Gmail consistently emphasizes sender reputation as the cornerstone of email deliverability. This reputation is meticulously built on a foundation of consistent positive user engagement, adherence to bulk sender guidelines, and robust email authentication protocols. While subdomains can offer strategic advantages for segmentation, their reputation remains intrinsically linked to the overall sending practices of the parent domain. Documentation implicitly, and often explicitly, warns against sending to disengaged users, highlighting that a cautious and quality-focused approach to new IP and subdomain warm-up is crucial. Providers encourage leveraging tools like Google Postmaster Tools to monitor performance and identify potential issues early.
Key findings
- Sender reputation critical: Gmail's filtering systems heavily rely on sender reputation, which is influenced by spam complaints, bounce rates, and active user engagement (opens, clicks, replies).
- Engagement metrics: Mailbox providers prioritize senders whose emails are consistently opened and clicked, using these engagement signals to determine inbox placement.
- Subdomain relationship: Even when using subdomains for email marketing deliverability, their reputation is linked to the parent domain and the overall quality of sent mail.
- Warm-up principles: New IP and domain warm-up processes should involve a gradual increase in volume, starting with highly engaged subscribers to build a positive sending history.
Key considerations
- Compliance: Strictly adhere to bulk sender guidelines provided by major mailbox providers to maintain a good sending reputation and avoid being blocklisted.
- Feedback loops: Utilize feedback loops provided by ISPs to quickly identify and remove users who mark emails as spam, preventing further negative impacts.
- Authentication: Ensure proper implementation of email authentication protocols, including SPF, DKIM, and DMARC, for all sending domains and subdomains to build trust with receiving servers.
- Gradual scaling: Increase sending volume slowly and consistently, especially during a migration, allowing mailbox providers to assess your sending behavior and build trust in your new sending infrastructure, as outlined in official Google Postmaster Tools guidance.
Technical article
Google Postmaster Tools states that a high spam rate or numerous direct spam complaints will significantly degrade your sending reputation. This degradation leads to more of your messages being classified as spam by their filtering systems. Maintaining low complaint rates is therefore crucial for inbox placement and overall sender health.
Technical article
Microsoft's Outlook.com Postmaster guidelines emphasize that senders must maintain rigorous list hygiene, sending only to genuinely engaged users to avoid being blocked. Sending to unengaged or invalid addresses can quickly lead to negative reputation scores and prevent your emails from reaching the inbox. Regular list cleaning is thus a non-negotiable best practice.
Related resources
2 resources
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