Welcome to the forums,
Admins can set these attributes via CLI on COS or individual user:
zimbraMailMessageLifetime (default is 0 disabled - careful with this one as it affects mail in any folder)
zimbraMailSpamLifetime (default is 30d)
zimbraMailTrashLifetime (default is 30d)
These as well, though currently not exposed in the user's UI:
zimbraPrefInboxReadLifetime
zimbraPrefInboxUnreadLifetime
zimbraPrefSentLifetime
zimbraPrefJunkLifetime
zimbraPrefTrashLifetime
The one's currently exposed in the admin console gui > cos/user > advanced tab:
zimbraMailMessageLifetime
zimbraMailSpamLifetime
zimbraMailTrashLifetime
There's also:
Bug 20753 - Allow user to set chat folder lifetime
Vote for / support ticket tag / cc watch:
Bug 6229 - Individual Folder Max Messages and Max Lifetime