[Dovecot] Sieve fileinto a subfolder fails

[Rich McAllister]

I'm using Dovecot 1.0.10 on Ubuntu 8.04, using the packages from the
distro; exim4 is my MTA and it's configured according to the
instructions in the wiki, everything is working fine for delivery into
the Maildir INBOX via Dovecot's LDA and reading mail via IMAP using
Thunderbird.

My habit on previous mail systems was to create a Lists folder and
subfolders under Lists for each mailing list I subscribe to.  I tried
to use Dovecot sieve to sort mail into the folders with sieve filters
like

require "fileinto";
if header :contains "Subject" "[NCCC]" {
        fileinto "Lists/NCCC";
} else {
        keep;
}

I created Lists/NCCC via Thunderbird (so I could set the "check this
folder for new mail property") but when Dovecot tries to deliver into
the folder, I get the log message

 msgid=<...>: Couldn't open mailbox Lists/NCCC: Invalid mailbox name

If I use just

        fileinto "NCCC";

it works fine, going into a NCCC folder not in a subfolder as expected.

Is there some other syntax for specifying folder/subfolder names in
Dovecot sieve, or do I just have to live with the folders all at the
top level?
     	 
Rich


dovecot -n shows:

# 1.0.10: /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:/arda/export/mail/%u/Maildir
auth default:
  passdb:
    driver: pam
  userdb:
    driver: passwd