Summary
Poor email deliverability to Microsoft Outlook and Hotmail is a multifaceted problem stemming from issues with sender reputation, authentication, list hygiene, content, sending practices, and Microsoft's specific policies. A key factor is Microsoft's heavy reliance on sender reputation, influenced by IP/domain reputation, user engagement, and complaint rates. Authentication is crucial, with Microsoft prioritizing senders using SPF, DKIM, and DMARC. List hygiene is also critical, as sending to outdated or unengaged addresses leads to bounces and complaints. Content that triggers spam filters negatively impacts deliverability. Microsoft implements strict throttling policies and considers volume changes carefully. Shared IPs with poor reputations, and the lack of consistent sending patterns contribute to the issue. Monitoring blocklists, using SNDS, implementing feedback loops, warming up new IPs, A/B testing, and ensuring a properly configured reverse DNS record are vital for improving deliverability. Additionally, it's important to note that Outlook.com and Office365 may require slightly different strategies.
Key findings
- Sender Reputation: Microsoft prioritizes sender reputation (IP, domain, engagement) when filtering emails.
- Authentication: Proper SPF, DKIM, and DMARC authentication is essential.
- List Hygiene: Poor list hygiene leads to bounces and complaints.
- Content Quality: Spam triggers in content negatively impact deliverability.
- Throttling Policies: Microsoft implements strict throttling, especially for new IPs.
- Volume Sensitivity: Microsoft is sensitive to sudden changes in sending volume.
- Shared IP Risks: Shared IPs can suffer from the poor practices of other senders.
- Engagement: Low engagement signals unwanted email.
- Blocklist Impact: Being on a blocklist significantly impacts deliverability.
- Separate Platforms: Outlook.com and Office365 can behave differently.
Key considerations
- Monitor Reputation: Actively monitor your sender reputation using SNDS and other tools.
- Implement Authentication: Ensure correct SPF, DKIM, and DMARC configuration.
- Practice List Hygiene: Regularly clean your email lists.
- Improve Content: Avoid spam trigger words and ensure proper formatting.
- Warming Process: Gradually warm up new IPs.
- Consistent Volume: Maintain consistent sending volumes.
- Blocklist Monitoring: Actively check and address blocklist listings.
- Utilize SNDS: Regularly check and analyze the SNDS data.
- Implement FBL: Set up a Feedback Loop to handle complaints.
- rDNS Configuration: Ensure your reverse DNS record is correctly configured.
- A/B Testing: Perform A/B Testing to improve deliverability.
- Encourage Engagement: Encourage opens/clicks and get your users to move you from the junk folder or add to safe senders list.
What email marketers say
14 marketer opinions
Poor email deliverability to Microsoft Outlook and Hotmail is often attributed to a combination of factors related to sender reputation, authentication, list hygiene, content quality, and sending practices. Microsoft places a strong emphasis on sender reputation, which is affected by complaint rates, engagement metrics, and IP/domain history. Inconsistent sending volumes, shared IPs with poor reputations, and lack of proper email authentication (SPF, DKIM, DMARC) can negatively impact deliverability. Furthermore, content that triggers spam filters, poor list hygiene, and lack of user engagement contribute to the problem. Warming up IPs, consistent sending volumes and using A/B testing also improve deliverability.
Key opinions
- Sender Reputation: Microsoft heavily relies on sender reputation (IP, domain) when filtering emails. Poor reputation leads to deliverability issues.
- Authentication: Proper email authentication (SPF, DKIM, DMARC) is crucial for verifying your identity and improving deliverability.
- Complaint Rates: Microsoft is highly sensitive to spam complaint rates. High complaint rates can significantly damage your sender reputation.
- Volume Sensitivity: Microsoft is sensitive to sudden changes in sending volume. Spikes in volume can trigger spam filters.
- Engagement Metrics: User engagement (opens, clicks) plays a significant role. Low engagement can negatively impact deliverability.
- List Hygiene: Poor list hygiene (outdated, invalid addresses) contributes to bounces and complaints, hurting reputation.
- Shared IP Risks: Using a shared IP can be detrimental if other senders on the IP have poor sending practices.
- Content Quality: Email content containing spam trigger words or poor formatting can increase the likelihood of being filtered as spam.
Key considerations
- Monitor Reputation: Actively monitor your sender reputation using tools like Microsoft SNDS to identify and address potential issues.
- Implement Authentication: Ensure you have properly configured SPF, DKIM, and DMARC records for your sending domains.
- Clean Your Lists: Regularly clean your email lists to remove invalid, inactive, and unengaged subscribers.
- Improve Content: Optimize your email content to avoid spam trigger words and ensure proper formatting.
- Gradual Warm-up: If using a new IP address, gradually warm it up by increasing sending volume over time.
- Consistent Volume: Maintain a consistent sending volume to avoid triggering spam filters.
- Encourage Engagement: Encourage opens/clicks and get your users to move you from the junk folder or add to safe senders list.
- A/B Testing: Perform A/B testing to improve deliverability, by discovering what your user base likes and optimise subject lines and email content.
Marketer view
Marketer from Email Geeks shares that Microsoft has been more problematic than usual, starting around October 2019. Their support usually cites unusual activity or SmartScreen filter recommendations.
30 Mar 2024 - Email Geeks
Marketer view
Marketer from Email Geeks mentions if an IP is blocked by Microsoft (visible in SNDS), stopping all traffic to Microsoft domains for 2-3 days, then restarting with small amounts of traffic to engaged recipients is usually effective.
21 May 2025 - Email Geeks
What the experts say
4 expert opinions
Poor email deliverability to Microsoft's Outlook and Hotmail platforms is influenced by several factors. One key element is sender reputation, which encompasses IP and domain standing, along with user engagement levels. Low engagement metrics on Hotmail, such as poor open and click-through rates coupled with high complaint rates, can negatively impact deliverability. Additionally, Outlook.com and Office365 should be treated differently concerning deliverability strategies. Furthermore, it is important to actively monitor blacklists and maintain high sender reputation.
Key opinions
- Sender Reputation Focus: Microsoft heavily prioritizes sender reputation when determining email placement, including IP/Domain reputation and user engagement.
- Engagement Metrics: Hotmail relies heavily on user engagement metrics (opens, clicks, complaints) for inbox placement decisions.
- Differentiated Platforms: Outlook.com and Office365 do not behave identically in terms of deliverability and require distinct strategies.
- Importance of Blocklists: Listings on major blocklists can severely impact deliverability to Microsoft platforms.
Key considerations
- Monitor Sender Reputation: Continuously monitor your IP and domain reputation to identify and address any potential issues.
- Improve Engagement: Implement strategies to increase user engagement (opens, clicks) and reduce complaint rates.
- Address Platforms Individually: Develop distinct strategies tailored to the nuances of Outlook.com and Office365 for optimal deliverability.
- Monitor Blocklists: Check regularly for blocklist listings, and take steps to be removed immediately.
Expert view
Expert from Word to the Wise explains that Microsoft places a heavy emphasis on sender reputation. This includes factors like IP address reputation, domain reputation, and user engagement. If these are low, your deliverability to Outlook/Hotmail will be impacted.
3 May 2023 - Word to the Wise
Expert view
Expert from Word to the Wise recommends actively monitoring blocklists, as a listing on a major blocklist can severely impact your deliverability to all email providers, including Microsoft. Regularly check your IP and domain against popular blocklists.
15 Oct 2024 - Word to the Wise
What the documentation says
4 technical articles
Microsoft employs several mechanisms to protect its users from spam, impacting email deliverability. Throttling policies limit the volume of emails, especially from new IPs or domains. Monitoring IP reputation is crucial, and Microsoft provides the Sender Network Data Services (SNDS) tool for this. Implementing a Feedback Loop (FBL) allows senders to receive and act on spam complaints. Finally, a properly configured reverse DNS record (PTR) is essential for deliverability.
Key findings
- Throttling: Microsoft implements strict throttling policies, which can negatively impact deliverability, especially for new IPs or domains sending large volumes.
- SNDS Tool: Microsoft offers the Sender Network Data Services (SNDS) tool to monitor IP reputation, allowing senders to identify and address deliverability issues.
- Feedback Loop (FBL): Implementing an FBL is vital for receiving spam complaints and removing subscribers marking emails as spam.
- Reverse DNS (PTR) Record: A properly configured reverse DNS record (PTR) is essential for verifying the sender's identity and improving deliverability.
Key considerations
- Monitor Throttling: Be aware of Microsoft's throttling policies, especially when starting a new campaign or using a new IP or domain.
- Utilize SNDS: Regularly monitor your IP reputation using Microsoft's SNDS tool.
- Implement FBL: Implement a Feedback Loop (FBL) to promptly address spam complaints.
- Configure rDNS: Ensure your reverse DNS record (PTR) is correctly configured and matches your sending IP address to your domain name.
Technical article
Documentation from Microsoft Support explains that they implement strict throttling policies to protect their users from spam. Sending large volumes of email in a short period, especially from new IPs or domains, can trigger throttling and impact deliverability.
14 Nov 2021 - Microsoft Support
Technical article
Documentation from RFC explains that having a properly configured reverse DNS record (PTR record) that matches your sending IP address to your domain name is very important for deliverability. Ensure your rDNS record is properly setup.
14 Oct 2022 - RFC
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