[Dovecot] Can't create subfolders of my INBOX or delete folders with IMAP

[Matthew Exon]

Hi,

I've been using the dovecot IMAP server for about a year now, and 
basically it works.  But there's an annoying problem, that I can't make 
any subfolders.  I can only make folders that are at the same level as 
my INBOX folder.  Worse, I can't delete folders once I've created them.

I'm using Debian unstable on both the server machine and my client 
machine.  The dovecot version is 0.99.13.  For my mail client, I'm using 
Mozilla Thunderbird version 1.0.

I've done a bit of investigation on my filesystem, and by googling for 
all kinds of stuff, but I'm really drawing a blank on this particular 
problem.  Most of the general linux email documentation I've found 
either doesn't mention IMAP, or doesn't mention dovecot, or both.  I can 
barely find any references to the concept of "subfolder" at all.  I 
really don't want to know anything about email servers, I just want the 
bloody thing to work.  Trying to figure out what the hell's going on is 
really frustrating!

On the server, I seem to have various mailboxes distributed around the 
place.  I've got a mail box in /var/spool/mail.  I've got a file ~/mbox, 
which seems to be very old and is therefore probably a red herring. I've 
also got a directory ~/Mail with a bunch of files in, one for each of my 
folders.  Having some of my mail in /var/spool, and some in my home 
directory, seems a really horrible way of arranging things, but anyway...

Various online sources seem to suggest that maildir is better than mbox. 
  I don't have any particular preference for one or the other, but I 
don't want to change if I don't have to because:

1) From experience, I don't screw with settings if I don't have to. 
Debian made it that way, and changing it behind Debian's back is a 
surefire way to cause trouble later.

2) Any other accounts on that machine (especially ones I might create in 
future) will probably still be mbox, causing even worse confusion later.

3) Porting mailboxes is always risky, and I don't want to lose my mail, 
or have incoming email dropped, or accidentally corrupt it, or anything 
like that.

So I'm not going to do any of that unless I'm sure that it's actually 
going to fix the subfolder problem, and until now I haven't found any 
information anywhere to guarantee that that's the case.  Intuitively I 
can guess that if a folder is just a big file full of concatenated 
email, then making a subfolder is going to be pretty much impossible, 
but I don't want to guess here.

The actual symptoms in thunderbird are:

When I select "New folder...", I get the "Create as a subfolder of:" 
dropdown hierarchy box thingy, but the "Inbox" option is greyed out 
(side complaint: no user interface should ever have a greyed out option 
without providing an explanation as to why it's not available, and what 
you should do if you want it to be available.  Displaying it like that 
is just cruelly teasing the user).

When I try to delete a folder, I get a dialog box saying "The current 
command did not succeed.  The mail server responded: Mailbox doesn't 
exist: <name of folder>".  This is pretty frustrating, because I can 
*see* the damn thing in thunderbird.  (another side complaint: "The 
current command"?  You're *running* the bloody command, you should have 
a better description than that!)

For some reason though, I can rename a folder with no problems.

I went into /var/log/ on the server, to see what was in the Dovecot log 
file about the server errors above, but there *is* no log file, nor 
anything in the syslog.  That can't be good.  How do you tell the 
sysadmin when there's a problem?

Does anyone have any suggestions for how I can fix this?  And if 
possible, I want to fix this the Debian way, that is by modifying a 
debconf setting or a /etc/default file or something like that, so that 
when I upgrade Debian, or uninstall dovecot and then reinstall it, it'll 
be handled gracefully.

Thanks,
Matthew Exon