I have dedicated server Debian 4, and webmin 1.450 / virtualmin 3.66. I use postfix+dovecot pair. So my problem is that I can create from mail-client like (Thunderbird for example)folders, but I cannot create sub folders in this folders. So how I can fix it on working system?
Thanks for any answers!!
What error do you get in the log when you try to create a sub-folder?
(I don’t even know if IMAP supports sub-folders, as I don’t believe I’ve ever tried to make one…but it seems likely that it would support them.)
I don’t see any messages about subfoldaer creation in syslog…
Seems like I use mbox instead maildir…
So how I can change it in webmin if I have existing mailusers
If you’re using mbox (which isn’t the Virtualmin default if you used the install.sh script), that means Postfix and procmail would both need to be reconfigured to deliver using maildir, and that you also have to convert all the current users’ email.
While I haven’t had to do this before, there’s a thread that points out instructions that someone said worked for them.
Again, I’ve never used these instructions, and please be sure to have a backup of everything before making any changes 
http://www.virtualmin.com/index.php?option=com_fireboard&Itemid=77&func=view&catid=8&id=19582