Just a tip.. whatever is not (yet) available via the webclient can be achieved (with some work indeed..) by being creative and using outlook or firebird connector: In case of outlook you get pst-files in/with which you can copy folders around easily. Other things like bulk deleting messages somewhere 'in between' timespans etc. are also pretty easy using 'alternative' mailfiles. In some cases you may need to recreate the/a account from pst via importer etc.
Not always best method but pretty easy for common admin 'special'tasks..:0)
Maybe this helps,
Using ZCS Network-edition 5.0.16 on Ubuntu 6.06.2 LTS and 8.04 LTS