Why is Microsoft Defender marking my one-to-one emails as spam with a high SCL score when authentication is correct and there are no blacklist issues?

Email marketer from Reddit shares that even with perfect setup, Microsoft's algorithms are sensitive to content and engagement. He suggests A/B testing different subject lines and body content, and also ensuring recipients are actively engaging with the emails (not just ignoring or deleting them).

Marketer from Email Geeks suggests trying different subject lines, friendly from addresses, removing external domains from the message, and removing the body content by dichotomy to identify the cause of the high SCL score.

Email marketer from Microsoft Community suggests that even with proper authentication (SPF, DKIM, DMARC), Microsoft Defender may still flag emails as spam due to content filters or the reputation of the sending IP address. They recommend checking if the sending IP is listed on any Microsoft blocklists and ensuring that the content of the emails doesn't trigger spam filters.

Email marketer from Mailjet explains that sender reputation, determined by factors like IP address and domain history, greatly influences deliverability in Microsoft Defender. They advise monitoring sender reputation tools (like SNDS) and maintaining consistent sending volumes to build trust.

Email marketer from Validity explains that implementing a feedback loop allows Microsoft to notify you when recipients mark your emails as spam. This information can then be used to identify and remove problematic subscribers, improving your overall sender reputation.

Email marketer from Sendinblue shares that for new sending domains or IPs, a proper warm-up process is critical to establish a positive reputation with Microsoft. Incrementally increase sending volume over time to avoid triggering spam filters. This is less relevant for established IPs.

Marketer from Email Geeks asks if the customer is using the domain exclusively for the described activity, including subdomains, and offers to provide insights if the domain is shared privately.

Email marketer from MxToolbox, shares that checking common blacklists is always a good idea. Although the question mentions no blacklist issues this tool will help find ones that others don't.

Email marketer from GlockApps Blog states that Microsoft Defender performs advanced content analysis. Avoid using URL shorteners, excessive use of certain keywords, and spam trigger words in both the subject and body of the email. Use of tracking pixels may cause issues too.

Email marketer from Reddit explains that if you are using shared hosting, the IP reputation of the server can be impacted by other users on the same server. They recommends using a dedicated IP address for sending emails.

Email marketer from EmailListValidationHQ, says that regular list cleaning can help deliverability. Removing old, inactive, or invalid email addresses from your list and help improve engagement rates.

Email marketer from StackExchange explains that the lack of positive engagement (opens, clicks) with your emails can negatively affect your sender reputation with Microsoft. Microsoft uses engagement metrics to determine whether to send mail to the inbox or junk folder. She suggests improving engagement by sending relevant content to engaged users.

Expert from Email Geeks explains that an SCL of 9 indicates a high probability of spam and suggests the issue is likely not a false positive. He suggests sharing more details about the identity, business model, sending mechanics, address acquisition, mail content, and other senders from the domain to speculate on the cause.

Expert from Word to the Wise explains that Microsoft's junk mail filter is affected by more than just authentication. The content, sending infrastructure, and recipient engagement also play a role. It may be necessary to perform more investigation to see if the content or sending behavior is out of line.

Expert from Word to the Wise suggests that Microsoft's filtering of one-to-one emails as spam, despite authentication, could be related to content triggers, sending patterns, or recipient interaction. They mention looking at things like the URL reputation, and content that may be suspicious to Microsofts algorithms.

Documentation from Microsoft explains the Smart Network Data Services (SNDS) program allows senders to monitor the health and reputation of their sending IPs on the Microsoft network. This provides visibility into complaint rates and spam trap hits, which can help diagnose deliverability issues.

Documentation from Microsoft clarifies that Microsoft uses internal and external reputation lists to identify source IPs that may be sending spam. Poor IP reputation, even if not on public blocklists, can cause messages to be flagged as spam.

Documentation from Microsoft explains that the SCL (Spam Confidence Level) values are assigned by the Exchange Online Protection (EOP) service. Higher SCL values indicate a higher probability that a message is spam. An SCL of 9 means the message is almost certainly spam.