OK. I am trying to think in terms of searches... but:
1. In Zimbra everything can be in the INBOX as sorting is done by searches, but if I then use IMAP/Outlook does Zimbra make virtual IMAP folders for Outlook to see so that the email is sorted?
2. Let's say we try Zimbra and the test users decide it just doesn't do what we need. How would you dump the giant Zimbra inbox to a proper set of sorted IMAP files/folders?
3. Supposing we ultimately migrate a horde of users to Zimbra. They had their nice IMAP folders and such. Assuming we figure out how to retain the integrity of the mappings in the migration, how do users then APPLY NEW FILTERS to start NEW folders to existing emails?
As I am just starting to look at this, it seems Zimbra is a one-way ticket. It would be easier to adopt if migration to and from was simplified. My guess is personally, I'll keep using folders for this very reason. (Also, having a couple ways of finding something helps my brain.... why do a search when you know the message is one of the five most recent in the folder?)