Let us know if you need help on how to set those.
Zmprov - Zimbra :: Wiki
For instance on the COS named 'default':
su - zimbra
zmprov mc default zimbraPrefSentLifetime 30d
Or on an account:
su - zimbra
zmprov ma
user@domain.com zimbraPrefSentLifetime 30d
Account level will use the COS value unless explicitly set otherwise, then account level overrides COS.
This is all dependent on the new zimbraMailPurgeSleepInterval in v5 (the actual 'cleanup') which has a default of 1min to process roughly 1440 accounts/day.
See this thread for more info:
[SOLVED] junk mail cleanup