ClearOS 5.2 There should be a way to specify auto-purging for mail quarantine, e.g. delete messages older than X days old.

Source:

There is a "quarantine-purge" script that will automatically delete messages older than 30 days. On a ClearOS 5.1/5.2 system, run the following to grab the latest version of the quarantine software:

yum upgrade mailzu

Then run "quarantine-purge". Feel free to configure a cron job for this too of course.