Why do new IPs remain red in Microsoft SNDS during warming?
Matthew Whittaker
Co-founder & CTO, Suped
Published 6 Jun 2025
Updated 19 Aug 2025
7 min read
Warming up new IP addresses can be a critical, yet often frustrating, process for email senders. A common challenge arises when new sending IPs remain stubbornly red in Microsoft Smart Network Data Services (SNDS), even after days or weeks of consistent, controlled sending. This persistent red status can be unsettling, leading senders to question if their warming strategy is effective or if they are facing a deeper issue.
The appearance of a red status in Microsoft SNDS for new IP addresses is a common experience, not necessarily an immediate cause for alarm. It reflects the cautious approach Internet Service Providers (ISPs) take with new sending infrastructure. Understanding why this happens and what to expect is key to navigating the IP warming process successfully, especially with a vigilant provider like Microsoft.
The nuances of Microsoft SNDS reputation
Microsoft's Smart Network Data Services (SNDS) provides senders with data on their IP reputation and email health, primarily displaying a red, yellow, or green status. While these indicators are helpful, they are not the sole determinants of inbox placement or a perfect reflection of deliverability.
It's important to remember that a red status on SNDS, particularly for a new IP, indicates Microsoft's initial assessment of an IP with no prior history or established positive sending patterns. New IPs are inherently viewed with skepticism. They lack the positive reputation built over time by consistent, low-complaint sending. During this initial phase, even if your email volume is low and targeted at engaged users, Microsoft may assign a red status as a default protective measure.
The SNDS system aggregates various spam filtering results and may show a red flag if your IP is blocked due to abuse complaints. However, the color in SNDS may not perfectly align with actual filtering outcomes at times. This discrepancy can be particularly noticeable during the early stages of warming. You might observe some mail still reaching the inbox despite a red SNDS status, or conversely, poor deliverability even with a green status.
Why new IPs start red and stay red longer at Microsoft
New IP addresses lack a sending history, meaning Microsoft has no pre-existing data to trust. This absence of a positive reputation often defaults to a 'red' or suspicious status until proven otherwise. It’s their way of protecting users from potential spam or malicious activity.
Microsoft is known for its stringent filtering policies, especially during the initial days of IP warming. Unlike some other mailbox providers that might quickly transition new IPs, Microsoft may take longer to acknowledge positive sending patterns. This extended period in the 'red' zone is a common frustration for senders.
Even with an existing, reputable domain, new IPs are evaluated independently. While the domain's reputation can eventually aid the new IPs, it doesn't instantly transfer the trust. This means you effectively start building trust from scratch for each new IP, regardless of your established brand.
Key factors influencing Microsoft's IP reputation
While SNDS colors are a visible indicator, Microsoft's filtering decisions are based on a complex interplay of various factors. Understanding these elements is crucial for successful IP warming and overall deliverability.
Sender authentication: Correct implementation of SPF, DKIM, and DMARC is foundational. These protocols verify that your emails are legitimate and prevent spoofing. Failures in these areas can quickly land new IPs on a blocklist or in the spam folder.
Recipient engagement: Positive engagement signals, such as opens, clicks, and replies, tell Microsoft that your mail is desired. Conversely, a lack of engagement, or worse, high rates of deletions without opening, can harm your reputation.
Spam complaints: Even a small number of spam complaints on a new IP can have a disproportionately negative impact. Microsoft is very sensitive to this signal, as it directly reflects user dissatisfaction. Make sure to monitor your Junk Mail Reporting Program (JMRP) to track these.
Bounce rates: High bounce rates, especially hard bounces, indicate poor list hygiene and can signal suspicious activity. Keep your email lists clean and verified. You might want to refer to our guide on why your emails are going to spam for more insights.
Even with robust authentication and low complaints, the content of your emails can influence deliverability. Avoid spammy keywords, excessive images, or poor formatting that might trigger spam filters.
It's a multi-faceted evaluation process, and the SNDS red status is just one piece of the puzzle. Focusing on all these elements will contribute to a faster reputation build.
Strategies for effective IP warming with Microsoft
Patience and consistency are paramount when warming new IP addresses, especially with Microsoft. If you're seeing a persistent red status, maintaining your low-and-slow approach is often the best course of action. This signals to Microsoft that you are a legitimate sender building a responsible sending pattern.
Continue sending to your most engaged subscribers first. These are the recipients most likely to open your emails and least likely to mark them as spam, generating positive engagement signals. Gradually increase your volume to this highly engaged segment before expanding to broader audiences. This measured approach helps build trust progressively. We have a detailed guide on why new IPs take longer to warm if you want to dive deeper into this.
While SNDS might be red, monitor your actual deliverability to Microsoft accounts closely. Look for trends in open rates, click-through rates, and bounce rates. These real-world metrics often provide a more accurate picture of your email performance than just the SNDS color alone. If after a month of consistent, careful sending the status doesn't change and deliverability remains poor, then it might be time to investigate further, possibly by contacting Microsoft support. For a broader perspective, you might find our article on contradictions between SNDS data and deliverability useful.
Views from the trenches
Best practices
Maintain a consistent, gradual increase in sending volume to build a positive reputation over time.
Prioritize sending to highly engaged subscribers first to generate positive engagement signals.
Continuously monitor your spam complaint rates and bounce rates to quickly identify and address issues.
Common pitfalls
Expecting immediate green status on SNDS for new IPs, as Microsoft is very cautious during warming.
Suddenly increasing email volume, which can trigger spam filters and lead to blocklisting.
Ignoring actual inbox placement and engagement metrics, focusing solely on SNDS color.
Expert tips
Consider pre-warming new IPs with highly whitelisted addresses before broader auto-warming.
If deliverability is consistently poor despite red SNDS and diligent warming, open a ticket with Microsoft support.
Remember that SNDS colors might not always perfectly reflect actual inbox placement; monitor other metrics.
Marketer view
Marketer from Email Geeks says they are battling this issue for weeks with their ESP and their next approach involves pre-warming with whitelisted addresses from Microsoft servers before opening it to auto-warming for all recipients.
2019-10-21 - Email Geeks
Expert view
Expert from Email Geeks says it takes time for new IPs to warm up and advises opening a ticket if no change is observed after a month of consistent sending.
2019-10-22 - Email Geeks
Navigating the warming process
Seeing new IPs remain red in Microsoft SNDS during warming is a common and often normal part of the process. Microsoft's strict reputation algorithms mean new IPs start with minimal trust and must earn their way to a positive status through consistent, high-quality sending. By focusing on gradual volume increases, targeting engaged recipients, and ensuring strong email authentication, you lay the groundwork for a solid sender reputation.
Microsoft Smart Network Data Services (SNDS), even after days or weeks of consistent, controlled sending. This persistent red status can be unsettling, leading senders to question if their warming strategy is effective or if they are facing a deeper issue.
