Do you have any directories starting wih "clamav" in /tmp ? If yes, delete them?
Yes, I deleted them but this did not help.
Do you have mbox files with a size > 0 in /var/spool/mail/ ?
I only have this problem with the account that had antivirus on. Now I have turned it off, but the quota keeps telling me that there account is full.
When I check the Maildir of the user ( /home/www/web13/user/hugo ) I see that there are no mails in new, cur and the other folders.
But when I do a quota check in Webmin it sais that the user used 16MB of space.