[Dovecot] Multiple mailboxes per user

[spam at wilysloth.com]

My users currently have mail delivered to mulitple MailDir locations  
via procmail.

~/mail/inbox/
~/mail/graph/
~/mail/spam/

I would like all these mailboxes to be exported via dovecot IMAP and  
appear as folders. However, I can't anything beyond the INBOX working.  
My approach is via 'namespaces'.

My config file is changed thusly:
$ sudo dovecot -n
# 1.0.15: /etc/dovecot/dovecot.conf
log_timestamp: %Y-%m-%d %H:%M:%S
login_dir: /var/run/dovecot/login
login_executable: /usr/lib/dovecot/imap-login
mail_privileged_group: mail
mail_location: maildir:~/mail/inbox
namespace:
   type: private
   inbox: yes
namespace:
   type: private
   prefix: graph
   location: maildir:~/mail/graph
namespace:
   type: private
   prefix: spam
   location: maildir:~/mail/spam
auth default:
   passdb:
     driver: pam
   userdb:
     driver: passwd

I try connecting with mutt and I can see the mails in 'inbox' just  
fine. I can also see (in the mutt browser) 'graph' and 'spam' just  
fine too:

y:Exit  c:Chdir  m:Mask  ?:Help
  1     IMAP                                  INBOX
  2     IMAP                                  graph.
  3     IMAP                                  spam.

However, selecting 'graph' I see:

y:Exit  c:Chdir  m:Mask  ?:Help
  1     IMAP                                  ../


...I would have expected it to open the 'graph' MailDir mailbox and  
display the mail.

I try connecting directly using 'mutt -f imaps://user@computer/graph'
and I see 'Invalid mailbox name'.

telnet-ing in:
$ nc localhost 143
* OK Dovecot ready.
a1 login user password
a1 OK Logged in.
c1 list "" *
* LIST (\HasNoChildren) "." "INBOX"
* LIST (\Noselect \HasChildren) "." "graph"
* LIST (\Noselect \HasChildren) "." "spam"
c1 OK List completed.
a100 logout
* BYE Logging out
a100 OK Logout completed.

The logs only show:
Oct 13 10:44:44 machine dovecot: imap-login: Login: user=<user>,  
method=PLAIN, rip=127.0.1.1, lip=127.0.1.1, TLS
Oct 13 10:44:46 machine dovecot: IMAP(user): Disconnected: Logged out

Any ideas where I am going wrong? Outlook Express also lists the  
'graph' and 'spam' folder but won't show their contents.

WS