Why has Microsoft email engagement dropped and how does throttling affect email deliverability?

Key findings

• Engagement versus deliverability: A drop in engagement (opens, clicks) doesn't always indicate a hard deliverability problem like being blacklisted or spam-foldering, especially if bounce rates remain steady. It can reflect user behavior changes.
• Widespread shifts: Broad societal changes, such as those seen during the pandemic, can alter how users interact with email, leading to lower engagement on certain platforms like Microsoft's webmail and mobile clients.
• Microsoft's unique behavior: Microsoft (including Outlook.com, Hotmail.com, Live.com) often exhibits different deliverability patterns compared to other ISPs like Gmail or Yahoo, sometimes showing disproportionately lower engagement or higher throttling. For more details, see why Microsoft email deliverability can be poor.
• Throttling as a signal: Throttling means an ISP temporarily delays your emails. While emails might eventually be delivered, persistent throttling is often a precursor to harsher measures like blocklisting or increased spam placement, indicating a need for intervention. This can be a sign that your email deliverability is at risk.

Key considerations

• Data granularity: For accurate diagnosis, analyze email performance by month, domain, and campaign to pinpoint specific drops rather than overall trends.
• Platform limitations: Be aware that some analytics platforms may not capture all open data from certain domains (e.g., Yahoo, Gmail), potentially skewing the perceived impact of other domains like Microsoft.
• Throttling interpretation: If throttling occurs, monitor whether emails are eventually delivered or result in a bounce. Consistent throttling without delivery indicates a serious issue. Microsoft's documentation on throttling and blocking clarifies their stance.
• Volume impact: High sending volumes are more likely to trigger throttling or other deliverability issues, especially if reputation is not stellar.

Key opinions

• COVID-19 impact: Some marketers link significant drops in Microsoft engagement to the coronavirus pandemic, suggesting a change in user behavior, particularly a decline in webmail and mobile engagement, leading to fewer opens and clicks.
• Microsoft's sensitivity: Microsoft's deliverability (especially for domains like Hotmail) can be 3-5 times worse than Gmail, Yahoo, Comcast, and iCloud, even without obvious spam-folding or blacklisting. More can be read about deliverability issues with Outlook and Hotmail.
• Throttling as a system change indicator: Throttling by Microsoft is sometimes attributed to system-wide changes on their end, affecting all managed IPs from certain ESPs. This is why it's important to monitor blocklists consistently.
• Bounce rate vs. throttling: Some distinguish between a 'true hard bounce' and a throttling error, noting that throttled emails may eventually be delivered, suggesting it is a less severe issue than an outright bounce.

Key considerations

• Holistic analysis: When investigating engagement drops, consider overall trends (e.g., higher opens but steady clicks during lockdowns) alongside specific domain performance.
• Suppressing users: If certain segments, like Microsoft users, consistently show low engagement, marketers may consider suppressing them from specific email campaigns to protect sender reputation.
• ISP communication: Engaging with your ESP or directly with Microsoft Postmaster services (e.g., SNDS and JMRP) can provide insights into system-wide issues or specific throttling reasons.
• Reporting accuracy: Ensure your ESP's reporting accurately distinguishes between temporary throttles and permanent bounces, as misinterpretation can lead to incorrect conclusions about deliverability. You can also monitor your own email open rates with our guide.

Key opinions

• Throttling as a warning: Throttling acts as a warning shot from the ISP, indicating that an email sender is at risk of being blocked in the near future. This emphasizes the urgency of addressing the root cause. This is a common strategy by ISPs, as seen with Yahoo's throttling practices.
• Precursor to blocking: Throttling typically occurs after an ISP has already been diverting a significant portion of a sender's mail to the spam folder, making it a critical sign of declining reputation.
• Deliverability is key: Even with high open rates, a lack of clicks or conversions can point to deliverability problems affecting inbox placement or user experience. This suggests that open rates alone are not a complete measure of success.

Key considerations

• Address throttling proactively: Do not treat throttling as merely a delay. It demands a thorough investigation into sender reputation, content quality, and authentication to prevent more severe consequences.
• Monitor spam folder placement: If you observe throttling, it's highly likely that a portion of your emails is already landing in the spam folder. Implement inbox placement testing to confirm this. This can be identified by understanding your email domain reputation.
• Review engagement metrics: Analyze click-through rates and conversion rates alongside open rates to get a holistic view of campaign effectiveness. High open rates with low clicks can still indicate content or deliverability issues.
• ISP-specific nuances: Recognize that each ISP, including Microsoft, has its own unique filtering algorithms and reputation thresholds. What works for Gmail might not work for Outlook. For additional insights, Spamresource provides valuable perspectives on current challenges.

Key findings

• New sender requirements: Microsoft, along with Gmail and Yahoo, is implementing new rules for bulk senders (5,000+ emails per day) to enhance security and user experience. Non-compliance will lead to emails being junked or blocked. You can learn more about Outlook's new sender requirements.
• Throttling as a punitive measure: Microsoft documentation explicitly states that if throttling does not prompt an administrator to remediate a persistently vulnerable server, email from that server will eventually be blocked. This underscores throttling as a serious warning, not just a benign delay. Microsoft's Tech Community explains throttling and blocking policies.
• Authentication standards: Improve deliverability to Outlook by implementing and correctly configuring SPF, DKIM, and DMARC. These authentication protocols help verify sender identity and build trust with Microsoft's filters. Read a simple guide to DMARC, SPF, and DKIM.

Key considerations

• Compliance for bulk senders: If you send 5,000 or more emails daily to Microsoft domains, strict compliance with their new rules is non-negotiable for inbox placement.
• Sender reputation management: Beyond technical setup, maintaining a good sender reputation through low complaint rates, high engagement, and minimal bounces is crucial for avoiding throttling and blocklisting. Klaviyo details deliverability best practices.
• Monitor feedback loops: Utilize Microsoft's Smart Network Data Services (SNDS) and Junk Mail Reporting Program (JMRP) to monitor your sending reputation and receive feedback on user complaints. This helps in understanding and mitigating issues that lead to throttling.