The Mailbox Purge Wiki entry mentions the following:
But what happens if one is set to ZERO (ie disabled)? Is ZERO shorter than 30d? Shouldn't admin settings trump user's settings?
When a mailbox is purged, all attributes are considered. In cases where there's both a system and user-level policy is specified for the same folder, the shorter interval is used.
By default, the following is set in our case, in particular for the Trash folder:
What we notice is that the Junk folder gets properly purged, however, the Trash folder does not. Most our users use a desktop client (Thunderbird).
zmprov ga firstname.lastname@example.org | grep -i Lifetime
Looking in the mailbox.log file, there is purge going on, but no way of telling which mailbox it is for - my guess it is the Junk folder as this one is getting purged:
SentLifetime works as we had a user that had tested an old copy of Zimbra desktop and somehow modified zimbraPrefSentLifeTime and messages in the Sent folder were getting purged.
2010-09-22 07:21:31,305 INFO [MailboxPurge] [email@example.com;mid=1883;] mailop - Deleting items: 279121,279122,279123,279124,279125,279126,279127,279153,279154,279155,279156,279157,279158,279159,279160,279161,279162,279163,279164,279165,279166,279167,279168,279169,279170.