1. Login to the web interface as administrator through URL : mail.yourdomainname.com
with administrator username with password
The email account need to have administrator privilege in order to adjust email
account disk space from Smartermail
2. Go to the last button of the top panel > Domain Settings
3. Select the Accounts on Left panel
4. Click on the email account from email account list.
5. Edit the Mailbox Size Limit (MB) and Save it.