I have a related question:
I'm having trouble using the Apple Mail client to create a new folder on the server. i get a message:
Mailbox Creation Failed
IMAP command “CREATE” failed.
Also, while I'm at it, this has nothing to do with Dreamhost, I think, but you say you use mail.app so i'll ask - I just started using mail.app after years of reading mail on servers with Pine. I can't get Rules to move mail to folders that are under the "IN" folder (i.e. on the server) - the dropdown in the rule creation dialog doesn't even show those subfolders, just the "IN" folder. I can't find anything in apple documentation about this. any ideas?