Spam / Phishing - Spam to the Microsoft Outlook Junk Folder

This article contains information on creating Microsoft 365 transport rules to direct emails flagged by Mimecast as spam to the Outlook Junk Folder by setting specific headers and spam confidence levels (SCL).

To create a transport rule in Microsoft 365 that directs emails with Mimecast's spam header to the Outlook Junk Folder, follow these steps:

 

Transport Rule Configuration

1. Access Exchange Admin Center:

• • • • Go to Microsoft 365 Exchange Admin Center.
      • Navigate to Mail flow > Rules, and click + Add a Rule.

2. Define the Rule:

• • • • Name: Move Spam to Junk
      • Conditions:

i. Select "A message header... matches this text."
ii. Enter the header name: X-Mimecast-Spam-Score.
iii. Specify the matching text: e.g., if the spam score exceeds a certain threshold like X-Mimecast-Spam-Score: 20 (you can adjust the threshold based on your preferences).

3. Set the Action:

• • • • Choose Modify the message properties... and select Set the spam confidence level (SCL).
      • Set the SCL to 9 to ensure the email will be treated as spam and placed in the Junk Folder. Please note that a value of 9 is based on the default Microsoft configuration. If you have changed the default configuration, then you should use the value you have configured.

4. Save the Rule:

• • • • Review and save the rule, ensuring it applies to inbound messages.

Considerations

• By using Mimecast's X-Mimecast-Spam-Score, you can target emails flagged with a specific spam score and categorize them automatically.
• Setting the SCL to 9 ensures Microsoft 365 classifies the message as spam and moves it directly to the Junk Folder in Outlook.