From Kolab Wiki
With the Kolab Server you can define user quota for a Kolab account.
Administrators, maintainers and domain maintainers are allowed to set/change user hard quota; e.g. with the Kolab webadmin. If the quota field is empty, the user has no disk limit. If a user exceed his quota limit, all emails will rejected and no data can be saved in the IMAP folders of this account.
You can list all accounts with their current used disk space and their defined quota with the command (with root or kolab-r):
If a user exceed a defined percentage of his used disk space, the user get quota warnings at regular intervals until his disk space is again under the limit. Only administrators can define this percentage in the webadmin; default is 80%. The value is true for all Kolab users. The default warning interval are 24 hours and can change in the /kolab/etc/kolab/kolabquotawarn (line my $warninterval = 60*60*24;).