Before running the first backup operation, assign content to the default subclient.
From the navigation pane, go to Protect > Applications > Exchange.
The Exchange page appears.
Click an Exchange database.
The Exchange Database page appears.
In the Subclient section, click default.
The default page appears.
In the Content section, click Edit.
The Subclient content dialog box appears.
Select the databases that you want to assign to the default subclient, and then click Save.
What to Do Next
Specify the backup source for the default subclient.