I've never heard of that function before, this is one of the things I love about this forum, you get to find out new things! Personally, I'd never use such a thing as I keep my email tightly organised and to me, 200+ folder sounds like a nightmare. I am quite sure though, that to those users, my way of organising email would seem insane. Each to their own
As to what can be done about it, well, the function is not currently in Zimbra, but could be added in a number of ways, perhaps by adding an alphabet ladder to the left of the folder list in a similar way to how the address books work. You would need to add a request for enhancement for this in the bugzilla.
Other than that, I'd say offer outlook back to the most important users and see if the rest can learn new tricks?