Summary
Microsoft blocks cold emails due to a combination of factors relating to sender reputation, authentication, content, and recipient engagement. Sending unsolicited emails without consent leads to complaints and a damaged reputation, especially if recipients mark them as spam. Microsoft's SmartScreen filter actively analyzes these factors to determine filtering or blocking. A poor IP address reputation from previous spam activities, being listed on blocklists, and failing to properly authenticate emails using SPF, DKIM, and DMARC all contribute to deliverability problems. Additionally, low engagement rates, hitting spam traps, sending to outdated lists, lack of personalization, using URL shorteners, inconsistent sending patterns, and aggressive sending frequencies can trigger Microsoft's spam filters. Monitoring blocklists and participating in feedback loops help identify and address issues. If Microsoft is blocking all outgoing emails entirely, then contact your ISP.
Key findings
- Consent is Critical: Sending unsolicited emails without consent is a primary cause of being blocked.
- Sender Reputation Matters: Microsoft's filters heavily rely on sender reputation to determine email deliverability.
- Authentication is Essential: Properly configured SPF, DKIM, and DMARC are essential for authenticating emails and preventing spoofing.
- Engagement Impacts Deliverability: Low engagement rates (opens, clicks) negatively affect deliverability.
- List Hygiene is Important: Sending to outdated or invalid email addresses damages sender reputation.
- Blocklists Cause Issues: Being listed on a blocklist used by Microsoft will cause your emails to be blocked.
- Sending patterns affect delivery: Aggressive sending patterns damage reputation and filters will block your emails
- ISP issues: If all your emails are being blocked, this could be an issue between you and your ISP.
Key considerations
- Obtain Recipient Consent: Prioritize gaining explicit consent before sending any emails.
- Monitor Sender Reputation Regularly: Monitor your IP address and domain's reputation and address any issues promptly.
- Implement Proper Authentication Protocols: Ensure SPF, DKIM, and DMARC are correctly configured for your domain.
- Focus on Recipient Engagement: Craft engaging and relevant content to boost open and click rates.
- Maintain Clean Email Lists: Regularly clean your email lists to remove invalid and inactive addresses.
- Monitor Blocklists Proactively: Check if your IP address/domain is listed on any blocklists used by Microsoft.
- Establish Consistent Sending Habits: Adhere to consistent sending patterns to avoid triggering spam filters.
- Avoid Spam Traps: Implement practices to avoid sending to spam trap addresses.
- Personalize Emails: Personalize emails to improve engagement and avoid spam filters.
- Avoid URL Shorteners: Use full, direct URLs in emails to reduce the likelihood of being flagged as spam.
- Implement Feedback Loops: If possible, participate in feedback loops with Microsoft to address recipient complaints and improve deliverability.
- Contact ISP: If all your emails are being blocked, this could be an issue between you and your ISP.
What email marketers say
11 marketer opinions
Cold emails are often blocked by Microsoft due to a combination of factors related to sender reputation, email authentication, and engagement. Sending unsolicited emails, especially without proper consent, leads to complaints and negatively impacts your sender reputation. Poor IP address reputation from previous spam activities, failure to properly authenticate emails using SPF, DKIM, and DMARC, and low engagement rates all contribute to Microsoft's filters identifying your emails as spam. Additionally, hitting spam traps, sending to outdated email lists, a lack of personalization, the use of URL shorteners, and aggressive sending frequencies can also result in blocked emails.
Key opinions
- Consent and Complaints: Sending unsolicited emails without consent results in complaints, which directly harms sender reputation.
- IP Reputation: A poor IP address reputation, often due to past spam activities, triggers Microsoft's spam filters.
- Email Authentication: Failing to properly implement SPF, DKIM, and DMARC makes emails appear suspicious and can lead to blocking.
- Engagement Rates: Low engagement (low open and click rates) signals that emails are unwanted, prompting Microsoft to block them.
- Spam Traps: Hitting spam trap email addresses severely damages sender reputation.
- List Hygiene: Sending to outdated or invalid email addresses harms sender reputation.
- Email Warmup: Sending too many emails too soon from a new IP can lead to being blocked. Gradual email warm up is required.
Key considerations
- Obtain Consent: Prioritize obtaining explicit consent before sending emails to avoid complaints.
- Monitor IP Reputation: Regularly check your IP address's reputation and address any negative issues promptly.
- Implement Authentication: Ensure SPF, DKIM, and DMARC are correctly configured to authenticate your emails.
- Improve Engagement: Focus on creating relevant and engaging content to encourage opens and clicks.
- Maintain List Hygiene: Regularly clean your email list to remove invalid and inactive addresses.
- Personalize Emails: Increase personalization to improve recipient engagement.
- Avoid URL Shorteners: Use full, direct URLs in emails to reduce the likelihood of being flagged as spam.
- Control Frequency: Implement a gradual email warm-up process and manage sending frequencies carefully.
- Monitor Blocklists: Proactively monitor blocklists to ensure that your IP address or domain is not listed.
Marketer view
Marketer from Email Geeks explains that if you're sending cold email, your first thought needs to be that complaints due to lack of permission are killing you. Rather than complying with Microsoft's policies requiring consent, you're trying to slide in by reducing volume. You should anticipate that they will notice and adjust their filters to meet your strategy.
16 Jul 2023 - Email Geeks
Marketer view
Email marketer from GMass explains that sending to outdated or invalid email addresses negatively affects your sender reputation. Regular list cleaning is crucial to avoid being blocked.
25 May 2025 - GMass
What the experts say
6 expert opinions
Microsoft blocks cold emails for several reasons, primarily tied to unsolicited sending and sender reputation. If Microsoft blocks all your outbound emails, it's an issue between you and your email provider. Sending unrequested emails at scale leads recipients to mark them as spam, negatively impacting sender reputation. This results in Microsoft correctly filtering emails. Monitoring blocklists is essential as being listed on one used by Microsoft directly leads to blocking. Maintaining consistent sending patterns is vital; spikes in volume or changes in sending habits can trigger filters. Actively participating in feedback loops with Microsoft helps identify and address recipient concerns, preventing further blocking.
Key opinions
- Unsolicited Emails = Spam: Sending emails people didn't ask for (cold emails) leads to recipients marking them as spam.
- Sender Reputation: Actions that negatively impact sender reputation (e.g., spam complaints) cause Microsoft to block emails.
- Blocklist Impact: Being listed on a blocklist used by Microsoft directly results in blocked emails.
- Sending Pattern Consistency: Inconsistent sending patterns or sudden volume spikes trigger spam filters.
- ISP Relationship: If your email sending is cut off completely it could be an issue between you and your ISP.
Key considerations
- Avoid Unsolicited Emails: Prioritize permission and avoid sending emails to recipients who haven't requested them.
- Monitor Blocklists: Regularly check if your IP/domain is on any blocklists used by Microsoft.
- Maintain Consistent Sending: Establish and maintain consistent sending patterns to avoid triggering filters.
- Implement Feedback Loops: If possible, participate in feedback loops with Microsoft to address recipient complaints.
- Address ISP issues: If you can't send emails from any address, contact your internet service provider to resolve.
Expert view
Expert from Email Geeks explains that if Microsoft is cutting off your ability to send mail out of their network, that's not a deliverability problem, that is between you and the company that you're paying money to. You'll need to ask them.
12 Oct 2022 - Email Geeks
Expert view
Expert from Word to the Wise explains that maintaining consistent sending patterns and good sender reputation is key. Sudden spikes in volume or changes in sending habits can trigger Microsoft's filters, especially when combined with cold emailing practices.
24 Jun 2022 - Word to the Wise
What the documentation says
4 technical articles
Microsoft's SmartScreen filter blocks cold emails based on sender reputation, content, and recipient complaints. Proper configuration of SPF records is crucial to specify authorized mail servers and prevent spoofing. DKIM signatures ensure email authenticity and prevent tampering. DMARC allows senders to define how receivers should handle emails failing SPF and DKIM checks, protecting against spoofing but requiring careful configuration to avoid blocking legitimate emails.
Key findings
- SmartScreen Filtering: Microsoft's SmartScreen filter assesses sender reputation, content, and recipient complaints to filter or block emails.
- SPF Authentication: SPF records authorize mail servers for a domain and prevent spoofing. Incorrect setup leads to deliverability issues.
- DKIM Authentication: DKIM signatures provide cryptographic verification of email authenticity and prevent tampering.
- DMARC Policy: DMARC allows senders to define how receivers should handle emails failing SPF/DKIM, protecting against spoofing.
Key considerations
- Monitor Sender Reputation: Be aware that Microsoft assesses and uses your sender reputation to determine your send limit.
- Configure SPF Records: Properly configure SPF records to specify authorized mail servers for your domain.
- Implement DKIM Signatures: Use DKIM signatures to ensure email authenticity and prevent tampering during transit.
- Set DMARC Policy: Carefully configure DMARC policies to protect against spoofing while avoiding the unintended blocking of legitimate emails. Monitor DMARC reports.
Technical article
Documentation from RFC explains that Sender Policy Framework (SPF) records specify which mail servers are authorized to send emails on behalf of your domain. Incorrect or missing SPF records make it easier for spammers to forge your email address, leading to deliverability problems.
18 Mar 2022 - RFC
Technical article
Documentation from Microsoft explains that their SmartScreen filter analyzes various factors, including sender reputation, content, and recipient complaints, to determine whether to block or filter emails.
31 Mar 2022 - Microsoft
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