What is referred to as 'condstore' is actually the feature-set that IMAP4Rev1 extension added in RFC 4551. It enables the quick synchronization of flags on messages as well as other conditional STORE operations.
I'm going to have to refer you to the RFC for the full details, but suffice it to say your Kolab 2.3 deployment could greatly benefit from enabling said extension on your mailboxes - it is not enabled by default as part of Cyrus IMAP 2.3, only with Cyrus IMAP 2.4 is the 'condstore' annotation set to 'true' by default.
You will have to execute two separate actions on your Kolab server:
You would preferrably execute these actions in this order, to reduce the chance new mailboxes are being created while you have not yet switched on 'condstore' to be enabled by default.
To enable condstore by default, in your favorite editor, add the following line to /kolab/etc/kolab/templates/imapd.conf.template:
Afterwards, write out new templates and reload Kolab with the new configuration;
To enable 'condstore' on existing mailboxes, login to Cyrus IMAP using the cyradm utility:
cyradm -t "" -u manager localhost
From there, you can examine one of the existing mailboxes;
localhost> info firstname.lastname@example.org
lastupdate: 12-Sep-2011 17:56:54 +0200
As you can see in the example, condstore has not yet been enabled for this mailbox. To enable condstore for a particular mailbox:
localhost> mboxcfg email@example.com condstore true
You will not want to repeat this command for all mailboxes, but instead use wildcard matching:
localhost> mboxcfg firstname.lastname@example.org condstore true
NOTE: The two commands do not return any output.
NOTE^2: Don't forget to, at your option, also enable condstore for mailboxes in the shared namespace, in other authentication realms, and perhaps even for those mailboxes that reside in the DELETED namespace (just in case they are restored to a visible namespace later on in life).