Hello,
We will try to enhance this feature in the upcoming versions.

The report displays amount of data transferred to the selected recipient(s) by the sender.
View the report from Monitor & analyze > Reports > Custom > Custom User Report > Sender’s Email Address > Recipient .
The bar graph displays amount of data transferred through each Email, while the tabular report contains the following information:
•Time: Date and Time in YYYY:MM:DD HH:MM:SS format.
•Subject : Subject line of the Email.
•User: Username of the sender as defined in the Device. If the User is not defined then it will display ‘Unidentified’ which means the traffic is generated by an unauthenticated user.
•Host: IP Address of the host.
•Destination: IP Address of the destination.
•Application/Proto:Port: Displays name of the application as defined in the Device. If the application is not defined, then this field will display the application identifier as a combination of protocol and port number.
•Size: Size of the Email.