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Ensure Spam confidence level (SCL) is configured in mail transport rules with specific domains

Remediation Considerations​

MaxScoreImplementationCostUserImpact
3UnknownUnknown

Remediation Impact​

Care should be taken before implementation to ensure there is no business need for case-by-case allow-listing. Modifying allow-listed domains could affect incoming mail flow to an organization although modern systems sending legitimate mail should have no issue with this. Note - While specifying the action for each domain, some options may entirely block mail from this domain

Remediation​

To modify SCL in mail transport rules so they do not allow any specific domains:

  1. Navigate to Exchange admin center https://admin.exchange.microsoft.com.
  2. Click to expand Mail Flow and then select Rules.
  3. For each rule that allows specific domains, set the spam confident level (SCL) to 0 or greater.
    • In "Do the following" section, select "Modify the message properties" and "set the spam confidence level (SCL)" and set to at least 0 (specifying the action for this domain, read more in the references attached below, some options may entirely block mail from this domain).

References:

  1. Spam confidence level | Microsoft Learn
  2. Best practices for configuring mail flow rules in Exchange Online | Microsoft Learn
  3. Mail flow rules (transport rules) in Exchange Online | Microsoft Learn