The steps to view the disk space usage of each email address in smartermail are as follow:

[1] Login into SmarterMail admin account.
[2] Now, click on Reports icon.
[3] Now, click on System Summary Reports.
[4] Now, click on Traffic Reports.
[5] Now, click on Disk Usage.
[6] Now, click on Domain name showing under Disk usage summary.
[7] You will see the username and their usage.