As part of configuration, you need to create a journaling rule in Microsoft 365 to allow email flow through the Email Security service.
A journaling mailbox is the mailbox that receives messages that match a journaling rule's conditions. Messages matching the rule's conditions are delivered to the journaling address specified in the rule.
You have a unique Email Security journaling address available to you in Email Security to create the journaling rule.
Important
A Microsoft 365 or Office 365 mailbox can't be used as a journaling mailbox.
Follow the steps below to add a journaling rule for Email Security to Microsoft 365.
- From the customer level in Email Security, go to Settings > Connections. 
- Under Step 2 Add a journaling rule to Microsoft 365, select More Details. 
- Select the  icon to copy your unique journaling email address. icon to copy your unique journaling email address.
- Go to https://purview.microsoft.com/datalifecyclemanagement/exchange 
- From the left menu, select Exchange (legacy) > Journal rules. 
- Select the  New rule tab. New rule tab.
- Paste the journaling email address copied in Step 3 into the Send journal reports to: field. 
- Under Journal messages sent or received from, select Everyone. 
- Under Type of message to journal, select All messages. The completed form should look as follows:  
- In the Journal rule name: field, enter a name for this rule. For example, Email Security. 
- Select Next and then Submit. 
 
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