Even though an email has been deleted from the user's email queue when using 3rd party email clients (Microsoft Outook, Windows Live Mail, Apple mail clients etc...) it may move into the trash area on the server, so still uses disk space on the hosting account. To delete a email permanently and free disk space it needs to be deleted from the trash area (empty trash) from the main webmail application (Roundcube).
To empty Trash from Roundcube webmail follow the steps below.
1) Login to your Roundcube webmail (see How To Login To Webmail )
2) Once you are in Roundcube webmail, click on Trash folder at your left navigation to make sure your Trash folder is being highlighted.
3) Click on the “Option *” Button at the bottom of the navigation and select “Empty”
empty trash roundcube
Your Trash folder should be empty by now. Complete the same process for the Junk mail, Sent mail or other folders, if utilized.
TIP: Your percentage of mail for the individual mail account used is displayed in a pie chart. If yours is at 5%, but another email account on your domain is at 85%, then in total the hosting account would be using 90% of disk space just for mail.