You have two options for logging into your admin mail account:
Log into the WebControlCenter at https://www.webcontrolcenter.com/domain.aspx
, and from the menu item go to MAIL > MAIL ADMIN, then click on LOGIN AS ADMIN.
Alternatively, you can go to http://mail.EXAMPLE.com to log in, where EXAMPLE.com is your domain name.
If you're logging via the second option shown above, you will need to log in using an admin email address and password. Otherwise skip to the next step.
1. From the top line menu items, select "Reports."
2. On the left column menu items, expand the "Domain Summary Reports" node.
3. From here expand "Traffic Reports".
4. Click on "Message Traffic".
5. This page will show you all the usage in descending order by their number of messages sent and received. To see a specific user's sending data, click on the user on this page.