To answer your question though, there are a lot of operational benefits to dynamic partitions. An obvious benefit is that partitioning simplifies replication. Another benefit is that it allows you to use alternative storage mechanisms, like maybe putting a partition on a CD-RW drive, and only bothering to make it available when you need to access it (this is what I was thinking about with the #Archive thing).
It's not necessary that partitions should map to NAMESPACE-advertised parts hierarchy at all. Cyrus allows mailboxes in the same hierarchy to live on different partitions. Replication is difficult even with this simplification (flag replication in particular looks like a colossal pain).
I can see why you might want filesystems and mailbox hierarchies to coincide, but the two aren't the same concept and shouldn't be trivially combined.
The #Archive thing is an interesting idea--but on some servers, "mounted" namespaces wouldn't be appropriate for the top level (i.e., Cyrus). They could also be handled inside the user's account, perhaps /home/tjs/archive/20040106/INBOX, for instance; maybe this is good, maybe it's not.
Anyway, I'm sorry this got a little picky. There are some other approaches that have a lot of merit, and I'm not sure NAMESPACE is the place to do these things.
Tim
