Step 1: Open Web site admin panel (https://:10000)
Step 2: Login to admin user account with password
Step 3: expand 'Servers' , click on 'Virtualmin Virtual Servers'
Step 4: click on your domain name (e.g. example.com)
Step 5: Expand section 'Quotas and limits' . You can check your web site quota (include database / mail / web site / FTP)
Step 6: you can click on button 'Edit Mail and FTP users' to check personal quota
Step 6: click on E-mail ,which you would like to check personal quota.
Step 7: Expand section 'Quota and home directory settings' for personal disk quota.
You can setup as 'unlimited'. Quota cannot excess the main disk quota.