It didnt really click until I had a "ls -ald *" on watch while I moved messages around folders using mdbox... I moved about 200 first to an Archive folder, and scratched my head wondering why i didnt see any new m.* files being created after the move. So then I moved some 5k other messages from other folders to my archive folder...
Then it dawned on me, how damn cool, the data never changes, dovecot just updates its index of what folder the message is in?! That is awesome! Also, I ended up answering my own question on the 2m mdbox_rotate_size, if a 10 meg email comes through it will write a 10 meg file, so thats cool too.
