Why are my cold emails being blocked by Microsoft?

Key findings

• Spam complaints: The primary reason cold emails are blocked is often due to high complaint rates. When recipients mark your emails as spam, Microsoft's filters learn to identify and block your future mailings.
• Lack of consent: Microsoft's policies heavily emphasize explicit consent. Sending emails without a prior relationship or explicit opt-in can lead to blocks, regardless of sender volume.
• Sender reputation: A poor or declining sender reputation, often a consequence of low engagement, high bounce rates, or spam reports, significantly increases the likelihood of emails being blocked. Learn more about your email domain reputation.
• Authentication issues: Proper email authentication (SPF, DKIM, DMARC) is crucial. Microsoft increasingly blocks emails from domains that lack proper authentication, seeing them as potential phishing or spoofing attempts. For a simple overview, see our guide to DMARC, SPF, and DKIM.

Key considerations

• Define "cold email": For email service providers like Microsoft, any unsolicited email, regardless of intent, is often categorized as spam. This definition is critical to understanding why your emails are blocked. Learn more about what constitutes spam.
• Policy adherence: Attempting to bypass Microsoft's policies (e.g., by lowering volume without addressing consent issues) will likely be detected and lead to further blocking.
• Source of sending: If you are using a third-party service provider to send your cold emails, Microsoft might block emails originating from their network due to broader reputation issues or specific security concerns (e.g., related to vulnerabilities like CrowdStrike).

Key opinions

• Volume control is insufficient: Simply reducing the number of emails sent per day (e.g., 35 emails/day) or per domain is often not enough to prevent blocking if the underlying issue of unpermissioned sending remains.
• Recipient actions drive blocking: Emails are blocked primarily because recipients mark them as spam, signalling to Microsoft that the mail is unwanted.
• Cold email equals spam: Many marketers reiterate that "cold email" is simply a euphemism for spam, as it involves sending unsolicited messages, which is against best practices and often provider policies. Our article, Why are my cold emails going to spam? explains this further.
• Sender reputation impact: High bounce rates and rejections significantly damage sender reputation, leading to more emails being blocked or filtered to spam folders.

Key considerations

• Compliance over tactics: Focusing on compliance with Microsoft's consent-based policies is more effective than trying to find technical loopholes or minor adjustments to sending volume.
• Impact on legitimate senders: Unsolicited emailing makes it harder for everyone else to achieve inbox delivery for requested emails, contributing to negative industry stereotypes.
• Platform limitations: Using platforms not designed for cold emailing (e.g., Mailchimp) can lead to policy violations and harm your sender reputation. Refer to our guide on How to Comply With Outlook's New Sender Requirements.

Key opinions

• Permission is paramount: Complaints stemming from a lack of explicit permission from recipients are the primary cause of cold email blocking by Microsoft.
• Adapting filters: Microsoft's filters are dynamic and will adjust to counter sender strategies that attempt to circumvent consent requirements, making volume reduction alone ineffective. This aligns with why your emails might be blocked by Microsoft domains.
• Cold email is spam: Experts firmly categorize unsolicited commercial email (cold email) as spam, emphasizing that legitimate email marketing is permission-based. This is crucial for understanding why Microsoft Outlook is blocking your emails.
• Filtering is working as intended: When Microsoft routes cold emails to the spam folder, it indicates their systems are successfully protecting users from unwanted mail.
• Bulk sender rules apply: Microsoft's restrictions specifically target bulk senders, those sending 5,000 emails or more to Outlook.com, Hotmail.com, and Live.com domains.

Key considerations

• Deliverability is not the issue: If Microsoft is actively blocking your ability to send mail from their network, it is a policy enforcement issue, not a typical deliverability problem, requiring direct engagement with your email service provider.
• Ethos of email marketing: Sending unsolicited emails goes against the fundamental principles of respectful and effective email communication. More insights are available on Word to the Wise.
• Authentication for trust: Ensuring your domain is properly authenticated (with SPF, DKIM, and DMARC) is a baseline requirement to build trust with Microsoft's systems.

Key findings

• Bulk sender thresholds: Microsoft specifically imposes restrictions on bulk senders, defined as those sending 5,000 or more emails daily to Outlook.com, Hotmail.com, and Live.com domains.
• Authentication mandates: Proper configuration of SPF, DKIM, and DMARC is essential. Issues with these records can directly trigger DMARC verification failures, leading to blocks.
• Unsolicited is spam: According to definitions adopted by security organizations, spam is unsolicited and unwanted junk email, primarily sent for commercial purposes. Microsoft's filtering reflects this definition.

Key considerations

• Policy enforcement: Microsoft's systems actively manage inbound email, and non-compliance with their policies, especially around authentication, results in blockages. This can be why your emails are not delivering to Microsoft inboxes.
• Sender reputation metrics: Microsoft analyzes various factors, including sender reputation, bounce rates, and complaint rates, to determine inbox placement. A high rate of bounces and rejections is a clear signal of poor reputation.
• DMARC failure causes: Email forwarding and misconfigurations in sender SPF, DKIM, and DMARC records are often cited as the primary reasons for triggering DMARC verification failures, leading to emails being blocked.