Summary
Hotmail's email blocking is multifaceted, stemming from issues within the sender's network infrastructure, email content, reputation, authentication practices, and recipient engagement. Microsoft extensively examines sender networks, scrutinizing third-party providers, image hosting, and shared resources. Maintaining impeccable list hygiene by avoiding spam traps and ensuring valid email addresses is critical. Proper email authentication with SPF, DKIM, and DMARC is a necessity. Sender reputation is paramount; low engagement, high complaint rates, and manual emails without unsubscribe options can lead to severe deliverability problems. Monitoring IP reputation via SNDS and JMRP, consistent sending patterns, and strong opt-in practices are also essential.
Key findings
- Network Scrutiny: Microsoft delves deep into sender networks, examining third-party providers, image hosting, and shared resources.
- Authentication Imperative: Failing authentication checks (SPF, DKIM, DMARC) is a primary reason for Hotmail blocking emails; proper setup and validation are essential.
- Reputation Matters: Low sender reputation, often due to poor list hygiene and low engagement, leads to blocks.
- List Hygiene: Hitting spam traps, sending to invalid addresses, and general poor list hygiene severely damage sender reputation.
- Engagement Factor: Low recipient engagement (low open rates, clicks) can negatively impact deliverability.
- Manual Email Risks: Manual emails lacking unsubscribe options are a significant cause of blocking.
- Aggressive Filtering: Hotmail's filtering is very aggressive and is complex. Focus on following email marketing best practices and the results will improve over time.
Key considerations
- 3rd Party Audit: Thoroughly audit third-party providers, ensuring their practices align with deliverability best practices.
- Network Hygiene: Monitor network infrastructure for any potential issues, including shared resources that could harm reputation.
- Monitor IP Reputation: Regularly monitor IP reputation using SNDS and JMRP.
- Clean Email Lists: Consistently clean email lists, removing inactive subscribers and potential spam traps.
- Ensure Authentication: Verify that SPF, DKIM, and DMARC are correctly configured and validated.
- Improve Engagement: Enhance email content to increase recipient engagement, boosting open rates and reducing spam complaints.
- Opt-In Processes: Strengthen opt-in processes to ensure subscribers actively want to receive emails.
- Reverse DNS Settings: Ensure sending IPs have valid reverse DNS records.
What email marketers say
8 marketer opinions
Hotmail blocks emails for various reasons including poor IP reputation due to spam, low engagement from recipients, presence on blacklists, hitting spam traps, unauthenticated emails, manual emails without unsubscribe options, and incorrect reverse DNS records. Resolutions include maintaining clean email lists, improving engagement through relevant content, removing spam traps, authenticating emails with SPF, DKIM, and DMARC, monitoring IP reputation via SNDS, and ensuring correct rDNS configuration.
Key opinions
- IP Reputation: A poor IP reputation, often due to sending spam, can lead to Hotmail blocking emails. Monitoring and maintaining a clean IP are crucial.
- Engagement: Low engagement from recipients (e.g., not opening or clicking emails) can negatively impact deliverability to Hotmail.
- Authentication: Failing authentication checks (SPF, DKIM, DMARC) is a primary reason for Hotmail blocking emails.
- List Hygiene: Hitting spam traps and sending to invalid addresses can severely damage your sender reputation with Hotmail.
- Manual Emails: Sending manual emails without proper unsubscribe mechanisms can lead to blocking, especially if recipients mark them as spam.
- rDNS Records: An incorrect or missing reverse DNS (rDNS) record for your mail server can cause Hotmail to reject your emails.
Key considerations
- SNDS Monitoring: Regularly monitor your IP reputation using Microsoft's Smart Network Data Services (SNDS) to identify and address deliverability issues.
- Content Relevance: Ensure your email content is relevant and engaging to recipients to improve open rates and reduce spam complaints.
- Blacklist Checks: Periodically check if your IP address is blacklisted and take steps to remove it if necessary.
- List Cleaning: Implement a robust list cleaning process to remove inactive or invalid email addresses and avoid spam traps.
- Authentication Setup: Properly configure and validate your SPF, DKIM, and DMARC records to authenticate your emails.
- Unsubscribe Options: Ensure all emails, including manual ones, have clear and easy-to-use unsubscribe options to comply with email marketing best practices.
Marketer view
Email marketer from SenderScore shares that hitting spam traps can severely impact deliverability to Hotmail. Regularly clean your email lists to remove inactive or invalid addresses to avoid spam traps.
10 Aug 2022 - SenderScore
Marketer view
Email marketer from Reddit explains that emails are going to spam because Hotmail is being too agressive. They share that you should check blacklists and use a service like mail-tester to check your score. They also mention that it will slowly improve over time.
31 Dec 2022 - Reddit
What the experts say
7 expert opinions
Hotmail's blocking of emails can stem from various factors related to network infrastructure, brand reputation, email content, and user engagement. Microsoft delves deep into sender networks, considering third-party providers, image hosting, and shared resources. Maintaining clean lists, avoiding spam traps, authenticating emails, and focusing on opt-in practices are crucial. Reputation is key, as poor list hygiene and low engagement trigger blocks. Microsoft considers content, reputation, and user engagement metrics when filtering. Manual emails without unsubscribe options are problematic. Microsoft is capable of tracking subdomains and IPs used across different ESPs. Focusing on network hygiene and opt-in practices is crucial.
Key opinions
- Network Infrastructure: Microsoft examines the network space around senders, including third-party providers, image hosting, and shared resources (ASNs, SWIPs, domains, CDNs).
- Brand Reputation: Microsoft uses brand-level filtering, and deliverability can be affected by different divisions of the same company.
- Manual Emails: Manual emails without unsubscribe options are a significant issue, leading to blocking of all emails from the company.
- List Hygiene & Engagement: Poor list hygiene (spam traps, invalid addresses) and low engagement directly lead to reputation issues and blocks.
- Opt-in Practices: Strong opt-in practices are crucial for building and maintaining a positive sender reputation.
- Email Authentication: Proper email authentication (SPF, DKIM, DMARC) is crucial, because this confirms that the messages are not suspicious.
- Tracking Capabilities: Microsoft can track subdomains and IP addresses used across different ESPs, allowing them to connect sending behaviors.
Key considerations
- Third-Party Vetting: Thoroughly vet all third-party providers used by the client, including those for image hosting and tracking, to ensure they adhere to best practices.
- Network Monitoring: Monitor the network space around your sending infrastructure for any potential issues or shared resources that could negatively impact reputation.
- Email Authentication: Ensure SPF, DKIM, and DMARC are correctly configured and validated to authenticate your emails.
- Manual Email Policy: Implement a strict policy regarding manual emails, requiring unsubscribe options and adherence to email marketing best practices.
- List Cleaning: Regularly clean email lists to remove inactive subscribers and potential spam traps, reducing reputation risk.
- Engagement Enhancement: Focus on sending relevant and engaging content to encourage opens and clicks, improving overall sender reputation.
Expert view
Expert from Email Geeks explains that Hotmail is more sensitive to 'network effects', which include resources shared by multiple folks such as ASNs, SWIPs, domains, CDNs, and other services.
5 Apr 2025 - Email Geeks
Expert view
Expert from Email Geeks shares that Microsoft does a lot of digging into the network space around a sender and brand-level filtering, and that mail filtering can even be affected by where images are hosted.
5 Aug 2021 - Email Geeks
What the documentation says
4 technical articles
Improving email deliverability to Hotmail and other providers hinges on proper authentication (SPF, DKIM, DMARC), maintaining good sender reputation, and following email sending best practices. Key factors include consistent sending patterns, avoiding volume spikes, ensuring list hygiene, implementing feedback loops, monitoring sender reputation through tools like SNDS and JMRP, having valid reverse DNS records for sending IPs, and keeping complaint rates low.
Key findings
- Authentication: Proper authentication using SPF, DKIM, and DMARC is essential for verifying the legitimacy of your emails and preventing spoofing.
- Sender Reputation: Maintaining a good IP and domain reputation is crucial for avoiding blocks and spam filters.
- Sending Volume: Avoiding sudden spikes in email volume and maintaining consistent sending patterns helps establish trust and avoid triggering spam filters.
- List Hygiene: Ensuring proper list hygiene by removing invalid or inactive addresses reduces bounce rates and minimizes spam complaints.
- Feedback Loops: Implementing feedback loops allows you to identify and address issues that may be causing recipients to mark your emails as spam.
Key considerations
- SNDS Monitoring: Monitor your sender reputation using the Smart Network Data Services (SNDS) to gain insights into Microsoft's perspective on your sending practices.
- JMRP Participation: Participate in the Junk Email Reporting Program (JMRP) to receive reports of users marking your emails as junk, enabling you to identify and address potential issues.
- Reverse DNS Records: Ensure that your sending IPs have valid reverse DNS records, as this helps verify the legitimacy of your sending infrastructure.
- Complaint Rate Management: Keep complaint rates low by sending relevant and engaging content to recipients who have opted in to receive your emails.
- Internet Standards Compliance: Format your messages according to Internet standards to ensure compatibility and avoid triggering spam filters.
Technical article
Documentation from SparkPost explains that to improve deliverability to Microsoft, ensure proper list hygiene, implement feedback loops, and monitor your sending reputation through SNDS. Maintain a good IP and domain reputation by sending consistent volume and avoiding spam complaints.
26 Jun 2022 - SparkPost
Technical article
Documentation from Google Workspace explains how to prevent email to Gmail users from being blocked. They state that you should authenticate your email using SPF, DKIM, and DMARC. Ensure that sending IPs have valid reverse DNS records, keep complaint rates low and format messages according to Internet standards
28 Jul 2024 - Google Workspace
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