Summary
Microsoft email deliverability issues are unusually challenging due to a confluence of factors. Many senders are experiencing blocks and deliverability problems, even with established reputations. Underlying causes include poor sender reputation stemming from spam complaints, low engagement, sending to inactive email addresses, and technical setup issues like incorrect SPF, DKIM, and DMARC records. Microsoft's adaptive filtering systems respond to user behavior, so engagement metrics are crucial. Additional factors include sudden volume spikes without proper IP warming, poor list hygiene, content quality, potential IP blacklisting, and the complexity of Microsoft's filtering algorithms. Addressing these issues requires a multi-faceted approach, including implementing strong authentication (SPF, DKIM, DMARC), actively monitoring and improving engagement, practicing consistent list hygiene, carefully managing sending volumes, and closely monitoring sender reputation.
Key findings
- Reputation is Paramount: Sender reputation, influenced by engagement, complaints, and list quality, significantly impacts deliverability to Microsoft.
- Authentication is Essential: Proper SPF, DKIM, and DMARC implementation is critical for verifying sender identity and message integrity.
- Microsoft's Adaptive Filters: Microsoft's filtering system is adaptive and responsive to user behavior, making engagement a key signal.
- Volume Matters: Sudden volume increases without proper IP warming can trigger spam filters and damage reputation.
- List Hygiene is Non-Negotiable: Maintaining a clean and engaged email list is essential for positive sender reputation and deliverability.
Key considerations
- Implement Strong Authentication: Ensure SPF, DKIM, and DMARC are correctly configured for your sending domains.
- Boost and Monitor Engagement: Actively work to improve email engagement metrics (opens, clicks) and closely monitor user behavior.
- Practice List Hygiene Regularly: Implement a process for regularly cleaning your email lists to remove inactive, invalid, or unengaged addresses.
- Warm Up IP Addresses: If using a new IP address, gradually increase sending volume to establish a positive reputation.
- Monitor Sender Reputation Constantly: Use tools like Microsoft SNDS and third-party services to monitor your IP and domain reputation.
What email marketers say
13 marketer opinions
Microsoft email deliverability is currently facing challenges due to a combination of factors. Senders are experiencing blocks and filtering issues even with previously good reputations. Common causes include poor sender reputation stemming from spam complaints, low engagement, and sending to inactive addresses. Technical setup problems like incorrect SPF, DKIM, and DMARC records are also significant contributors. Additionally, Microsoft's complex filtering algorithms and adaptive systems respond to user behavior, making engagement metrics critical. Other factors include sudden volume spikes, poor list hygiene, content quality, and potential IP blacklisting. Maintaining consistent sending patterns, warming up IP addresses, monitoring sender reputation, and properly authenticating emails are recommended for improvement.
Key opinions
- Reputation Impact: Poor sender reputation due to spam complaints, low engagement, and inactive addresses affects deliverability.
- Technical Setup: Incorrect SPF, DKIM, and DMARC records contribute to deliverability issues.
- Microsoft Algorithms: Microsoft's filtering algorithms and adaptive systems respond to user behavior, heavily influencing deliverability.
- Volume Spikes: Sudden increases in email volume without proper IP warming can trigger spam filters.
- List Hygiene: Poor email list hygiene with invalid or inactive addresses negatively impacts sender reputation.
Key considerations
- Authentication: Implement and verify SPF, DKIM, and DMARC records to authenticate your email sending.
- Engagement: Monitor and improve email engagement metrics to signal positive sender reputation to Microsoft.
- List Maintenance: Regularly clean your email list to remove invalid, inactive, or unengaged addresses.
- Volume Control: Gradually warm up IP addresses and maintain consistent sending volume and frequency.
- Reputation Monitoring: Monitor your sender reputation and IP blacklists to identify and address deliverability issues proactively.
Marketer view
Email marketer from SendGrid recommends authenticating your emails with SPF, DKIM and DMARC. SendGrid also recommends warming up your IP address, cleaning your email list, segmenting your email list, and monitoring your sender reputation.
5 Mar 2025 - SendGrid
Marketer view
Email marketer from GlockApps shares tips to improve deliverability to Outlook and Hotmail, including authenticating your domain with SPF, DKIM, and DMARC, monitoring your IP and domain reputation, and segmenting your email list to send targeted content.
24 Sep 2022 - GlockApps
What the experts say
3 expert opinions
Microsoft email deliverability issues are widespread. Microsoft's adaptive filtering system considers user behavior, strongly influencing deliverability. Issues are caused by a combination of factors like sudden volume spikes, poor list hygiene, and negative engagement metrics.
Key opinions
- Adaptive Filtering: Microsoft's filtering system is adaptive and responds to user behavior, affecting deliverability.
- Engagement Impact: Engagement (or lack thereof) strongly influences Microsoft's filtering decisions.
- Combined Factors: Blocking is likely caused by sudden volume spikes, poor list hygiene, and negative engagement metrics.
Key considerations
- Persist and Engage: Continue efforts to improve deliverability, focusing on boosting engagement.
- Reduce Risky Data: Clean and refine email lists to remove potentially risky data.
- Monitor and Adjust: Warm up IP addresses properly and closely monitor sender reputation.
Expert view
Expert from Spam Resource answers that blocking is likely caused by a combination of factors like sudden volume spikes, poor list hygiene, and negative engagement metrics. It's important to warm up IP addresses properly and monitor sender reputation closely.
8 Jun 2024 - Spam Resource
Expert view
Expert from Email Geeks responds that Anne is not alone, advising to persist, boost engagement, and reduce risky data.
14 Dec 2021 - Email Geeks
What the documentation says
5 technical articles
To ensure email deliverability, particularly to Outlook.com and Gmail, senders must adhere to email authentication standards like SPF, DKIM, and DMARC. These protocols verify the sender's domain and message integrity, helping to prevent email spoofing and phishing. Compliance with email provider policies, maintaining low complaint rates, and following best practices for email content are also crucial. Monitoring sender reputation through tools like Google Postmaster Tools is recommended.
Key findings
- Authentication is Key: SPF, DKIM, and DMARC are essential for verifying sender identity and message integrity.
- Compliance Required: Complying with email provider policies and guidelines improves deliverability.
- Reputation Matters: Maintaining a positive sender reputation reduces the likelihood of emails being marked as spam.
Key considerations
- Implement Authentication: Set up SPF, DKIM, and DMARC records to authenticate your email domain.
- Monitor Reputation: Use tools like Google Postmaster Tools to monitor your sender reputation.
- Follow Best Practices: Adhere to best practices for email content to avoid triggering spam filters.
Technical article
Documentation from DKIM.org explains that DKIM (DomainKeys Identified Mail) is an email authentication system designed to verify the domain name of an email sender and the integrity of the message. DKIM uses cryptographic signatures to allow receiving mail servers to verify that an email message was sent by an authorized sender and has not been altered in transit.
14 Feb 2022 - DKIM.org
Technical article
Documentation from Google explains that in order to reach Gmail inboxes, you should authenticate your email, avoid spammy practices, and make it easy for users to unsubscribe. Google recommends monitoring your sender reputation in Postmaster Tools.
27 Apr 2023 - Google
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