Why are new email IPs taking longer to warm and remain in red on SNDS?
Matthew Whittaker
Co-founder & CTO, Suped
Published 16 Apr 2025
Updated 19 Aug 2025
8 min read
Recently, it feels like the email sending landscape has shifted. We've observed a noticeable change in how new email IPs behave during the warming process, particularly concerning their status in Microsoft's Smart Network Data Services (SNDS). What used to be a relatively predictable warming period now often sees IPs staying in the 'red' zone for longer, raising concerns about deliverability.
This extended 'red' status can be frustrating and confusing. It suggests a potential issue, yet sometimes email performance to non-Microsoft domains appears to be strong. This discrepancy leads many to question if something fundamental has changed in how mailbox providers, especially Microsoft, evaluate new sending infrastructure.
In this article, I want to explore the possible reasons behind this trend. We will look at how IP warming has evolved, what the SNDS 'red' status truly implies, and the factors that could be prolonging the warming phase. More importantly, we'll discuss strategies to navigate these challenges and ensure your emails reach the inbox.
The evolving landscape of IP warming
IP warming is a critical process for establishing a positive sender reputation with Internet Service Providers (ISPs) and mailbox providers. It involves gradually increasing the volume of emails sent from a new or previously unused IP address. This slow ramp-up allows providers to observe your sending habits and recipient engagement, building trust over time. Failing to warm an IP can lead to immediate blocklisting or high spam placement, severely impacting your email program.
Historically, a typical IP warming schedule might have seen an IP's reputation stabilize within a few weeks, with clear indications of progress through tools like SNDS. However, the current environment presents a more complex picture. ISPs are increasingly sophisticated in their filtering, using a wider array of data points beyond just volume to assess sender reputation.
The shift towards more aggressive filtering is partly a response to the ever-increasing volume of spam and phishing attempts. Mailbox providers are under pressure to protect their users from unwanted mail, which means new IPs are treated with greater suspicion until they prove their legitimacy. This heightened scrutiny can certainly prolong the warming period and make it harder to achieve a 'green' status quickly.
It's not just about sending volume anymore. Factors like recipient engagement, complaint rates, spam trap hits, and even specific content patterns play a much larger role. A new IP sending to an unengaged list, even at low volumes, will struggle to build the necessary positive reputation. This makes the warming process less about a rigid schedule and more about dynamic adjustments based on real-time feedback.
Deciphering SNDS red and its implications
Microsoft's Smart Network Data Services (SNDS) provides senders with data about their IP's reputation with Microsoft properties. The 'traffic light' system, with green, yellow, and red indicators, is a quick visual cue. Red typically signifies a high level of complaints or other negative metrics that could lead to emails being blocked or placed in the spam folder. However, as many experienced, the red status doesn't always perfectly align with actual deliverability. For more information, you can refer to discussions about SNDS data.
The prolonged red status in SNDS, even when other metrics look good, suggests that Microsoft's internal systems might be slower to update or have different thresholds compared to other mailbox providers. This could be due to their aggressive spam filtering algorithms or a more cautious approach to new IPs to prevent large-scale abuse.
It's important to remember that SNDS is just one tool among many. While a red status is concerning, it should be evaluated in conjunction with other deliverability metrics like inbox placement rates, open rates, and click-through rates. Sometimes, a red flag in SNDS might not translate to a complete block, but rather to increased throttling or placement in the junk folder.
Factors influencing prolonged warming and SNDS status
Several factors contribute to new IPs taking longer to warm and potentially staying in the red on SNDS:
List quality: Sending to unengaged or old lists is a primary reason for poor warming. High bounce rates, spam complaints, and low engagement signals can quickly trigger alarms.
Engagement metrics: Mailbox providers prioritize positive engagement (opens, clicks, replies). If recipients aren't interacting with your emails, it signals a lack of interest, leading to a negative reputation.
Content and sending practices: Spammy content, misleading subject lines, or poor formatting can negatively impact your reputation. Adhering to best practices for email deliverability is essential.
Microsoft's heightened filtering: As mentioned, Microsoft seems to have tightened its filtering mechanisms, making it tougher for new IPs to gain a good standing quickly. This might involve more aggressive throttling or a longer period of observation.
Lack of authentication: Proper SPF, DKIM, and DMARC configurations are fundamental. Without these, your emails are more likely to be flagged as suspicious.
If your new IP is struggling to warm up or remains stuck in red on SNDS, it's crucial to analyze your sending practices holistically. Sometimes, the problem lies not with the IP itself, but with the underlying data or content strategy. This is a common concern during new IP and subdomain warmup.
Strategies to expedite warming and improve SNDS standing
Typical IP warming (Old Experience)
Duration: Typically 2-4 weeks for most IPs to achieve good reputation.
SNDS status: IPs would quickly move from red to yellow, then green, reflecting progress.
Focus: Primarily on consistent volume increases and low complaint rates.
New IP warming challenges (Current Experience)
Duration: Can take 4-6 weeks or even longer, especially for Microsoft domains.
SNDS status: IPs may remain in red for extended periods, even if other providers show good standing.
Focus: Heavy emphasis on list hygiene, explicit opt-in, consistent engagement, and adherence to specific ISP best practices.
To effectively warm a new IP and improve its status on SNDS (and other monitoring tools), consider these strategies:
Clean your lists: Before starting, remove inactive users, bounces, and known spam traps. Send only to highly engaged subscribers. List quality is paramount for warming new IP addresses.
Segment your audience: During warming, focus on your most engaged segments first. This generates positive signals early on.
Gradual volume increases: Stick to a conservative warming schedule, increasing volume incrementally. Be prepared to slow down or pause if you see negative feedback.
Monitor feedback loops: Pay close attention to complaint rates. A high rate will quickly land your IP on a blocklist (or blacklist).
Engage Microsoft support: If your IP remains red despite following best practices, consider opening a mitigation ticket with Microsoft support for warming issues. Sometimes, manual intervention is needed.
Remember that the timeframe for IP warming can vary significantly. Patience and consistent monitoring are key. Even if SNDS shows red, focus on your overall inbox placement and engagement rates across all providers.
Views from the trenches
Best practices
Maintain exceptional list hygiene by regularly cleaning out inactive subscribers and known bounces. Quality over quantity is crucial.
Segment your audience and start warming by sending to your most engaged subscribers first. This builds early positive reputation.
Implement a slow and steady volume ramp-up, being prepared to adjust based on real-time feedback and metrics like open rates.
Ensure all email authentication protocols (SPF, DKIM, DMARC) are correctly configured and aligned for your sending domain.
Common pitfalls
Sending to old or unengaged lists, which leads to high bounces and spam complaints and triggers ISP filters.
Ignoring feedback loop data, especially for major providers, as this indicates subscriber dissatisfaction and reputation issues.
Attempting to rush the warming process by sending too much volume too soon, which often results in blocklisting.
Relying solely on SNDS status without correlating it with other deliverability metrics like inbox placement rates.
Expert tips
Sometimes, a manual mitigation ticket with Microsoft support is the only way to get a 'stuck' red SNDS status resolved.
If you see low open rates correlating with SNDS redness, it suggests the red status is meaningful and impacting deliverability.
Consider that Microsoft's filtering rules are constantly evolving and becoming stricter, requiring more diligent adherence to best practices.
The perfidious colors in SNDS don't always reflect immediate deliverability issues, but they do indicate a potential problem.
Marketer view
Marketer from Email Geeks says they have seen new IPs taking longer to move out of red in SNDS, and there might be a correlation with the actual engagement of the data, despite what the client claims.
2019-12-04 - Email Geeks
Marketer view
Marketer from Email Geeks says that sometimes SNDS gets stuck on red, and the only way to resolve it is by raising and escalating a mitigation ticket with Microsoft support.
2019-12-04 - Email Geeks
Navigating the evolving landscape of IP reputation
The challenges of warming new email IPs and dealing with prolonged 'red' statuses in SNDS reflect an ongoing evolution in email deliverability. Mailbox providers are becoming more stringent, demanding higher quality sending practices and consistent positive engagement.
While it might seem frustrating, this shift ultimately pushes senders towards better email hygiene and more relevant content, which benefits the entire email ecosystem. By focusing on list quality, engagement, and proactive monitoring, you can successfully navigate these challenges and ensure your emails consistently reach the inbox.
Microsoft properties. The 'traffic light' system, with green, yellow, and red indicators, is a quick visual cue. Red typically signifies a high level of complaints or other negative metrics that could lead to emails being blocked or placed in the spam folder. However, as many experienced, the red status doesn't always perfectly align with actual deliverability. For more information, you can refer to discussions about SNDS data.
