Summary
Email deliverability during a new subdomain warm-up can be perplexing, especially when initial open rates appear strong, yet subsequent emails land in the spam folder. This scenario, where a conservative warm-up schedule and proper authentication are in place but deliverability falters, points to factors beyond typical warm-up best practices. The distinction between reported open rates (which can be inflated due to privacy changes like Apple Mail Privacy Protection) and actual user engagement (clicks) is crucial. A low click-to-open rate can signal to Inbox Service Providers (ISPs) that recipients are not actively engaging with the content, despite merely opening it.
Key findings
- Open rate vs. engagement: High open rates, especially during initial warm-up, can be misleading. ISPs, particularly Gmail, prioritize actual engagement signals like clicks, replies, and emails moved from spam to inbox over simple opens, which may be influenced by privacy features. If recipients are not clicking or otherwise interacting, the emails may still be seen as low-value.
- Subdomain reputation: Even with correct SPF, DKIM, and DMARC records, a new subdomain has no established reputation. ISPs are cautious with new sending entities, requiring a gradual build-up of trust based on positive recipient interactions. This is why a proper subdomain warm-up is essential.
- Underlying issues: Problems can stem from historical issues with the client's brand, associations with known spammers (e.g., through affiliates), or problematic links within email content that trigger ISP filters. These deeper issues can override a sound warm-up strategy.
- Gmail postmaster tools limitations: Gmail Postmaster Tools may not report spam complaints for low sending volumes. This means senders might not be aware of initial negative feedback signals if they haven't reached certain (unpublished) thresholds.
Key considerations
- Adjust warm-up pace: While a schedule may have worked historically, ISPs' algorithms evolve. Consider reducing the initial send volume and the rate of increase, even if it seems overly conservative. For instance, increasing volume by 20-30% daily rather than doubling it can be safer. More information can be found in this Salesforce guide on IP warming.
- Focus on clicks: Prioritize recipient segments with a high click-through history for warm-up sends, rather than just high open rates. Gmail particularly values active engagement (e.g., clicks, replies, forwarding, moving from spam to inbox). If your emails are not generating clicks, your deliverability to Gmail will suffer.
- Investigate external factors: Thoroughly review the client's sending history, any associated third-party partnerships (like affiliates), and the reputation of linked domains. Negative associations can severely impact new subdomain reputation. A blocklist checker can also help identify if your domain or related IPs are listed.
- Patience and persistence: Warming up is a process of training ISP algorithms. Even if initial sends go to spam, consistently sending wanted mail at a manageable volume, focusing on engagement, can eventually improve inbox placement.
What email marketers say
Email marketers often encounter unexpected deliverability issues during subdomain warm-up, even when following what they consider to be conservative strategies. A key point of contention is the reliance on open rates, which may not accurately reflect true engagement. Many marketers share experiences where traditional warm-up methods, once successful, now face new challenges, particularly with major ISPs like Gmail. The discussion frequently revolves around balancing send volume, list segmentation, and the often-overlooked importance of click-through rates and other positive engagement signals.
Key opinions
- Open rates are misleading: Marketers frequently note that high open rates do not guarantee inbox placement, as ISPs like Gmail prioritize deeper engagement signals (like clicks) which are not skewed by privacy features that automatically open emails.
- Warm-up schedules may be too aggressive: Even seemingly conservative warm-up schedules, such as doubling volume daily, can be too aggressive for new subdomains, particularly with Gmail's sensitive algorithms. Some suggest much slower increments, like 20-30% daily.
- Beyond the schedule: Many marketers believe that if standard warm-up protocols are followed and issues persist, there are likely deeper, underlying problems at play, such as past domain history, affiliate relationships, or problematic links. These issues often go undiscovered until deliverability tanks.
- Segmenting by clicks: A strong opinion is to segment initial warm-up sends to the most engaged subscribers based on click history, not just open history. Gmail's algorithms heavily favor positive engagement signals.
Key considerations
- Verify engagement metrics: Marketers must understand that open rates are no longer the sole reliable indicator of engagement due to privacy features. Focus on clicks, spam complaints, and direct inbox placement feedback.
- Patience and persistence: Even with perfect setup, new subdomains need time to build trust. Marketers should be prepared for potential fluctuations in deliverability during the initial phases and persist with consistent, engaged sending.
- Review links and content: Check all links within emails for redirects or domains with poor reputations (e.g., EPS shared domains). Ensuring all links point to your own reputable domain can significantly improve deliverability. See our guide on why your emails fail.
- Assess client history: When facing unexpected deliverability drops, marketers need to dig into any hidden issues related to the client's past sending practices, data quality, or undisclosed affiliate programs that might be impacting sender reputation. For instance, consider why emails go to spam.
Marketer view
A marketer from Email Geeks shared their experience with initial warm-up emails showing incredibly high open rates (70-90%) but then plummeting to 1-3% on the second day with doubled volume, indicating immediate spam folder placement despite a conservative approach and established DNS authentication.
Marketer view
An email marketer from Email Geeks reported very low click-through rates (around 5%) for their initial warm-up sends, with some emails having zero clicks, which they acknowledged might be contributing to the deliverability issues despite good open rates.
What the experts say
Deliverability experts emphasize that while a warm-up schedule is important, it's often not the sole determinant of success, especially when initial volumes are very low. They point to the nuanced ways ISPs, particularly Gmail, assess sender reputation, focusing on genuine engagement beyond simple opens. Experts caution that underlying issues, such as undisclosed affiliate programs or poor historical domain health, can significantly derail even the most carefully planned warm-up efforts, leading to immediate spam flagging by sensitive filters. The consensus leans towards a deeper investigation into potential hidden problems and a longer, more patient approach to establishing trust.
Key opinions
- Engagement is key: Experts agree that ISPs like Gmail primarily assess positive engagement (clicks, replies, moves to inbox) over open rates, especially due to privacy changes affecting open tracking accuracy. Low click rates, even with high opens, indicate a lack of true interest.
- Warm-up volume: Some experts consider even small doubling increments (e.g., 20, 40, 80 emails) to be aggressive for a brand new reputation with Gmail. Others argue such low volumes are unlikely to be the primary cause of sudden spam placement, suggesting deeper issues.
- Hidden factors: A common expert opinion is that if a warm-up fails unexpectedly despite seemingly good practices, there are often undisclosed or overlooked factors at play, such as problematic affiliate relationships, poor list hygiene, or previous domain reputation issues catching up to the sender.
- Shared IPs and domain reputation: While some suggest checking for shared IP changes, many experts believe that for very low send volumes, shared IP pool changes or the general state of a shared IP are unlikely to be the root cause of sudden deliverability collapse. Instead, focus on the domain's unique signals. Our guide to understanding domain reputation can help.
Key considerations
- Holistic deliverability assessment: Beyond the warm-up schedule, experts advise a comprehensive review of all sending parameters: email content quality, link hygiene, subscriber acquisition methods, and any hidden historical issues that might predate the current warm-up.
- Slow and steady wins: Even if progress seems slow, consistent sending to highly engaged segments is critical for long-term reputation building. It’s a marathon, not a sprint, especially with challenging ISPs. For more, see our guide to improving email deliverability with domain warmup.
- Client transparency: Experts emphasize the importance of clients being fully transparent about all sending activities and partnerships. Undisclosed practices can lead to deliverability problems that are difficult to diagnose and resolve.
- Utilize postmaster tools: While Postmaster Tools might not provide granular FBL data at low volumes, they are invaluable for long-term monitoring of domain reputation, spam rates, and authentication errors once sufficient volume is achieved.
Expert view
An expert from Email Geeks suggested that the initial warm-up volume (e.g., 20 emails) is too low to establish a solid reputation quickly with ISPs. They emphasized the importance of ensuring DNS records like DKIM, SPF, and DMARC are robust before expecting deliverability to stabilize.
Expert view
An expert from Email Geeks argued that a warm-up starting at 20 emails and doubling daily is not overly aggressive, given the small total volume (less than 1000 emails). They concluded that such a rapid decline in deliverability indicates a deeper, more significant underlying problem rather than just a warm-up issue.
What the documentation says
Official documentation from email service providers and industry bodies consistently highlights that new domain warm-up is a critical, gradual process. It involves establishing sender reputation by sending desired emails to engaged recipients and carefully monitoring performance. Authentication (SPF, DKIM, DMARC) is foundational, but true inbox placement relies heavily on positive user engagement signals. Documentation often provides recommended warm-up schedules and emphasizes the evolving nature of ISP algorithms, which increasingly factor in recipient interaction to combat unwanted mail. It also implicitly states that sudden deliverability issues, even with low volumes, can indicate deeper policy violations or negative signals.
Key findings
- Reputation building: New domains and subdomains have no prior sending history, meaning they start with a neutral reputation. ISPs require a gradual increase in volume to build trust and demonstrate legitimate sending practices.
- Engagement signals: Beyond authentication, ISPs heavily weigh positive engagement (e.g., opens, clicks, replies, moving emails from spam to inbox) and negative engagement (e.g., spam complaints, unsubscribes) to determine inbox placement. High open rates alone are not sufficient.
- Gradual volume increase: Documentation consistently recommends a conservative, gradual increase in sending volume, often advising against rapid doubling, to allow ISPs time to assess the new sender's behavior and reputation.
- Content and list quality: The quality of email content and the cleanliness of the mailing list are paramount. Sending irrelevant or unwanted content, even to a small degree, can quickly damage a nascent reputation.
Key considerations
- Adhere to best practices: Ensure proper SPF, DKIM, and DMARC setup, as these are fundamental for establishing sender legitimacy and preventing spoofing. Our simple guide to DMARC, SPF, and DKIM can help.
- Monitor postmaster tools: Actively use ISP-provided tools like Google Postmaster Tools to monitor domain reputation, spam rates, and delivery errors, even if detailed feedback loops are not provided for low volumes. Our guide to Google Postmaster Tools V2 is a good place to start.
- Segment strategically: Begin warm-up by sending to the most engaged segments of your list to generate positive signals, before gradually introducing less engaged subscribers.
- Understand ISP thresholds: Be aware that ISPs have internal, unpublished thresholds for reporting data (like spam complaints) and for establishing reputation. Low volumes might not trigger full reporting, requiring a more intuitive approach to deliverability assessment.
Technical article
The HighLevel Support Portal recommends that their email sending guide is designed to help users avoid the spam folder and ensure emails land in the inbox, emphasizing email best practices and proper email warm-up as foundational steps for new senders.
Technical article
NotifyVisitors documentation highlights that when a new sender uses a new domain, they must undergo a warming process. This establishes their reputation as legitimate and trustworthy, preventing deliverability issues from the outset.
Related resources
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