Summary
New email IPs are taking longer to warm up and often remain in the 'red' status on Microsoft's SNDS due to stricter ISP scrutiny and an increased emphasis on immediate positive engagement. With no prior sending history, new IPs are highly vulnerable, meaning any initial missteps, such as sending to unengaged or invalid addresses, exceeding volume limits, or generating even a small number of complaints, can disproportionately damage their nascent reputation. This quickly pushes the IP into a problematic 'red' status that is difficult to clear, sometimes necessitating direct intervention with Microsoft support. This 'red' designation signifies a high likelihood of throttling and reduced deliverability, reflecting a tougher landscape for establishing sender trust.
Key findings
- Increased Difficulty: New email IPs are experiencing prolonged 'red' statuses on SNDS, indicating that the goalposts for IP warming have shifted and the process is now more challenging than in the past.
- ISP Scrutiny: ISPs, particularly Microsoft, treat new IP addresses with extreme caution due to their lack of prior sending history, making them highly susceptible to any negative signals from the outset.
- Impact of Early Signals: Even minor issues during the warm-up phase, such as sending to unengaged recipients, hitting spam traps, high bounce rates, or aggressive volume spikes, can disproportionately and immediately damage a new IP's reputation.
- Engagement Dependence: Mailbox providers heavily rely on recipient engagement signals, like opens and clicks, to build trust. Without this positive history, new IPs struggle to prove legitimacy, leading to a lingering 'red' status.
- Lingering Red Status: Once an IP falls into a 'red' status on SNDS, it is significantly more difficult and time-consuming to recover and build a positive reputation, sometimes requiring direct intervention.
- Correlated Deliverability: The 'red' status on SNDS is a meaningful indicator, often correlating directly with tangible deliverability issues such as throttling, low open rates, and general email suppression.
Key considerations
- Strategic Warm-up: Adhere strictly to a gradual IP warm-up schedule, as sending too much volume too quickly can immediately trigger anti-spam systems and damage reputation.
- Clean, Engaged Data: Prioritize sending to highly engaged, clean, and valid subscriber lists, especially during initial warm-up, to minimize bounces, complaints, and spam trap hits.
- Proactive Monitoring: Continuously monitor feedback loops, bounce rates, and engagement metrics, as even small percentages of negative feedback can disproportionately impact a new IP's fragile reputation.
- Remediation Readiness: Be prepared to adjust sending practices and potentially engage Microsoft support with a mitigation ticket if an IP remains 'red' on SNDS, as standard remediation efforts may not be sufficient.
What email marketers say
10 marketer opinions
Establishing a new email IP's reputation has become increasingly challenging, with new IPs frequently experiencing a prolonged 'red' status on SNDS. This challenge stems primarily from the complete absence of a prior sending history, which leads Internet Service Providers, especially Microsoft, to treat new IPs with extreme caution. Without an established positive reputation, any early negative signals-even minor ones like low engagement, a few complaints, or sending to bad addresses-are amplified disproportionately. This immediate negative feedback can quickly and persistently flag the IP as suspicious, making it difficult to achieve positive deliverability and requiring a much longer, more deliberate warm-up period to build trust.
Key opinions
- Protracted Red Status: The 'red' status on Microsoft's SNDS for new IPs is persisting for longer durations, indicating a tougher warming environment than in previous years.
- Absence of Reputation Buffer: New IPs operate without any established positive sending history, making them extremely susceptible to even minor negative signals.
- Disproportionate Impact of Early Errors: A small number of complaints, bounces, or low engagement during initial warm-up can cause severe, long-lasting damage to a new IP's nascent reputation.
- Microsoft's Elevated Caution: Microsoft's filtering systems are especially wary of new IP addresses, often requiring direct intervention or extended rehabilitation for IPs stuck in a 'red' state.
- Clear Correlation to Deliverability: A 'red' status on SNDS is a reliable indicator of actual deliverability challenges, including throttling and decreased open rates.
Key considerations
- Rigorous List Segmentation for Warm-up: Exclusively use highly engaged and meticulously clean segments of your subscriber list for initial IP warming to minimize negative signals.
- Proactive Engagement Cultivation: Focus on content and audience segments most likely to generate high opens and clicks during the warm-up phase to quickly build a positive sending history.
- Diligent Monitoring of Early Feedback: Closely track all feedback loops, bounce rates, and spam complaints from the very first sends, as even minor issues are highly detrimental to new IP reputation.
- Readiness for Direct ISP Escalation: Be prepared to open mitigation tickets or directly engage with Microsoft support if an IP remains persistently 'red' on SNDS despite adherence to best practices.
- Adjusted Expectations for Warm-up Duration: Recognize that the time required to warm a new IP has increased, demanding more patience and a sustained, careful approach to volume and list quality.
Marketer view
Email marketer from Email Geeks explains that the SNDS red status seems to hang around longer than 9-12 months ago and can correlate with the quality and engagement of data. They also note that it can get "stuck" on red, sometimes requiring a mitigation ticket with Microsoft support, and that the red status can correlate with increased likelihood of throttling and low open rates. They believe the goalposts for IP warming have moved and it is trickier now.
29 Apr 2025 - Email Geeks
Marketer view
Email marketer from Email Geeks shares that they have seen multiple people discussing SNDS being red recently, but have not personally observed significant upsetting signs beyond the red colors themselves.
6 Nov 2023 - Email Geeks
What the experts say
2 expert opinions
New email IPs are struggling to warm up and often remain in the 'red' on SNDS due to the extreme fragility of a fresh IP's reputation and the heightened importance of positive recipient engagement. Experts indicate that early missteps, such as hitting spam traps or targeting invalid addresses, can immediately create a negative reputation that is exceptionally difficult to reverse. Additionally, mailbox providers now critically assess user interaction, meaning new IPs must quickly demonstrate positive engagement through opens and clicks. Without this crucial positive feedback, and with any negative signals like complaints, the IP's standing will likely remain poor, prolonging its 'red' status.
Key opinions
- Fragile Early Reputation: New IP addresses are highly vulnerable, especially within their first 14 days, to quickly acquiring a poor reputation due to the absence of prior sending history.
- Impact of Negative Signals: Sending to invalid or spam trap addresses, or receiving complaints and bounces, disproportionately harms a new IP's nascent reputation, making recovery challenging.
- Recovery Difficulty: An initial negative reputation acquired by a new IP is exceptionally difficult and time-consuming to overcome, often leading to prolonged deliverability issues.
- Engagement as a Key Factor: Mailbox providers now heavily emphasize recipient engagement, such as opens and clicks, as a critical factor in building and maintaining a new IP's positive reputation.
- SNDS Reflection: A persistent 'red' status on Microsoft SNDS directly reflects a lack of positive engagement and the presence of negative signals, indicating a stalled warm-up and poor reputation.
Key considerations
- Strict List Hygiene: Utilize exceptionally clean and engaged subscriber lists for new IP warm-up to establish a positive sender reputation from the outset.
- Gradual Volume Increase: Implement a very slow and controlled ramp-up of sending volume to avoid triggering anti-spam systems and to allow reputation to build naturally.
- Prioritize Engagement: Focus on content and audience segments that are most likely to generate high levels of positive interaction, such as opens and clicks, which are crucial for reputation building.
- Avoid Negative Signals: Meticulously avoid sending to spam traps, invalid addresses, and anything that could lead to complaints or bounces, as early negative signals are disproportionately damaging and difficult to recover from.
Expert view
Expert from Spam Resource explains that new IPs can quickly acquire a poor reputation, particularly within the first 14 days, if they send to invalid or spam trap addresses. This initial negative reputation is very difficult to recover from, often leading to prolonged deliverability issues. He advises that new IP warm-up requires sending to exceptionally clean lists and a very gradual increase in volume to establish a positive reputation.
8 Oct 2024 - Spam Resource
Expert view
Expert from Word to the Wise explains that new IPs are taking longer to warm up because mailbox providers now heavily emphasize recipient engagement and sender history. Without sufficient positive engagement (like opens and clicks) and with any negative signals (such as complaints or bounces), a new IP will struggle to build a good reputation. This lack of positive signals can cause its standing, visible on tools like Microsoft SNDS, to remain low or 'red', as the speed of warming is directly tied to user interaction.
9 Aug 2023 - Word to the Wise
What the documentation says
5 technical articles
New email IPs are experiencing prolonged 'red' statuses on Microsoft's SNDS because they start with no pre-existing reputation, leading to immediate suspicion from ISPs. This makes them exceptionally vulnerable to any initial missteps. Sending too much volume too quickly, or to disengaged or invalid addresses, can instantly trigger anti-spam filters and damage the IP's fragile reputation, leading to a persistent 'red' status that signifies low trust. Recovering from this 'red' designation is an arduous process, demanding consistent, positive sending behavior to engaged recipients to gradually build the necessary trust with mailbox providers.
Key findings
- No Pre-existing Reputation: New IP addresses start with a 'blank slate,' meaning ISPs, including Microsoft, are highly suspicious of initial sending volumes due to a complete lack of established trust.
- Amplified Negative Signals: Any misstep during the initial warm-up, such as sending to unknown users, invalid addresses, or disengaged recipients, is amplified, quickly leading to a 'red' reputation status.
- ISP Anti-Spam Triggers: Aggressive sending patterns or suspicious volume from a new IP can immediately trigger ISP anti-spam systems, resulting in immediate damage to nascent reputation.
- Difficult Recovery from Red: Once an IP falls into a 'red' status on SNDS, it requires consistent sending of desired mail to valid recipients and extensive effort to re-establish trust and move to a positive standing.
- Engagement as a Trust Factor: Building a positive reputation is a slow process dependent on demonstrating consistent, positive sending behavior and high recipient engagement from the outset.
Key considerations
- Strict Warm-up Adherence: Follow a gradual IP warm-up schedule diligently, as exceeding volume limits too early will trigger anti-spam systems and immediately damage reputation.
- High-Quality List Use: Send exclusively to highly engaged, opt-in, and validated subscriber lists during the warm-up phase to foster positive engagement and avoid bounces or complaints.
- Continuous Performance Monitoring: Actively monitor feedback loops, bounce rates, and engagement metrics from the very first sends, as any negative signals are disproportionately harmful to a new IP.
- Patience and Persistence: Recognize that building a positive IP reputation is a slow and incremental process, requiring patience and sustained adherence to best practices to move out of a 'red' status.
Technical article
Documentation from Microsoft Learn explains that SNDS uses color codes (green, yellow, red) to indicate the health and reputation of an IP address. A "red" status signifies sending large volumes of mail to unknown or invalid users, or mail that is suspected of being spam. For new IPs, a lack of established reputation means any misstep in initial sending can quickly lead to a red status, and it takes consistent sending of desired mail to valid recipients to build a positive reputation and move out of the red.
24 Dec 2023 - Microsoft Learn
Technical article
Documentation from Twilio SendGrid explains that new IP addresses start with no pre-existing reputation, meaning ISPs (like Microsoft's Outlook.com/Hotmail) are highly suspicious of any significant volume. The warming process requires gradually increasing sending volume over time, sending to highly engaged users first. Any deviation, such as sending too much too soon or to disengaged recipients, can trigger spam filters and damage the nascent reputation, leading to blocklisting or a "red" status on services like SNDS.
9 Aug 2024 - Twilio SendGrid Documentation
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