Mailbox Purge Interval
Mailbox purging carries on continuously in the background. The process pauses/sleeps between each mailbox by a user defined interval (default is 1 minute). What's purged is defined in the Class of Service (COS) for a particular mailbox - see the Email Retention Policy on the Advanced tab in the admin console (it can be overridden for individual mailboxes in the Advanced tab of the account config).
To check the current setting (replace
host.domain.com as appropriate)...
zmprov gacf | grep zimbraMailPurgeSleepInterval
zmprov gs host.domain.com | grep zimbraMailPurgeSleepInterval
To set (I tend to set the interval so that all mailboxes get purged in a day)...
zmprov mcf zimbraMailPurgeSleepInterval 1h
To see purging activity see the mailbox logs, eg
grep 'purge' /opt/zimbra/log/mailbox.log z
grep 'purge' /opt/zimbra/log/mailbox.log.2012-08-05.gz