[Dovecot] dovecot is confused about mail_location

[Eric Raymond]

IMAP logins via fetchmail are failing on my mailserver

root at grelber:/home/esr# tail -f /var/log/mail.err
Nov 24 16:56:48 grelber dovecot: IMAP(cathy): mail_location not set and autodetection failed: Mail storage autodetection failed with home=/home/cathy
Nov 24 16:56:48 grelber dovecot: IMAP(cathy): Fatal: Namespace initialization failed
Nov 24 16:57:39 grelber dovecot: IMAP(cathy): mail_location not set and autodetection failed: Mail storage autodetection failed with home=/home/cathy
Nov 24 16:57:39 grelber dovecot: IMAP(cathy): Fatal: Namespace initialization failed
Nov 24 16:57:52 grelber dovecot: IMAP(cathy): mail_location not set and autodetection failed: Mail storage autodetection failed with home=/home/cathy
Nov 24 16:57:52 grelber dovecot: IMAP(cathy): Fatal: Namespace initialization failed
Nov 24 17:05:15 grelber dovecot: IMAP(cathy): mail_location not set and autodetection failed: Mail storage autodetection failed with home=/home/cathy
Nov 24 17:05:15 grelber dovecot: IMAP(cathy): Fatal: Namespace initialization failed
Nov 24 17:09:41 grelber dovecot: IMAP(cathy): mail_location not set and autodetection failed: Mail storage autodetection failed with home=/home/cathy
Nov 24 17:09:41 grelber dovecot: IMAP(cathy): Fatal: Namespace initialization failed

However:

root at grelber:/home/esr# dovecot -n
# 1.2.9: /etc/dovecot/dovecot.conf
# OS: Linux 2.6.32-24-generic x86_64 Ubuntu 10.04.1 LTS 
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: mbox:~/mail:/var/mail/%u
mbox_write_locks: fcntl dotlock
auth default:
  passdb:
    driver: pam
  userdb:
    driver: passwd

And cathy is a real user:

root at grelber:/home/esr# grep cathy /etc/passwd
cathy:x:1001:1001:Cathy Raymond,,,:/home/cathy:/bin/bash
oot at grelber:/home/esr# ls -l /var/mail/cathy
-rw------- 1 cathy mail 14296599 2010-11-24 17:30 /var/mail/cathy

Dovecot appears confused about whether or not mail_location is set.

Just to make matters more perplexing, when *I* fetch from IMAP - using a
fetchmail configuration identical except for username - it works.

This is driving me nuts.  Help?
-- 
		<a href="http://www.catb.org/~esr/">Eric S. Raymond</a>

"Taking my gun away because I might shoot someone is like cutting my tongue
out because I might yell `Fire!' in a crowded theater."
        -- Peter Venetoklis