problems with quota files

[Riccardo Veraldi]

Hello I am running cyrus 2.4.17

I realized that quota shown for users with quota command is much less 
than real filesystem usage

an example:

/usr/lib/cyrus-imapd/quota user.username
    Quota   % Used     Used Root
  15000000       34  5189501 user.username

du -sh /var/spool/imap/m/user/username
11G    /var/spool/imap/m/user/username

I am a bit worried about it.

I am using ext4

the same problem was also on the previous cyrus version I was using 
2.3.16  because I have the same problems.

I fixed the quota files with quota -f but it did not resolve my problem.

any hints ?

thank you

Rick