[Dovecot] userdb didn't return a home directory with v1.1.7

[Ivars Strazdiņš]

Hi all,
I am running Dovecot v1.1.7 in a relatively quiet and calm environment. 
Suddenly overnight cron job has started throwing out errors like:
/usr/sbin/dovecot --exec-mail ext /usr/lib/dovecot/expire-tool

Error: userdb(user1 at mail.example) didn't return a home directory
Error: userdb(user2 at mail.example) didn't return a home directory

Indeed, running this command produces:
-------------------------
$ sudo /usr/sbin/dovecot --exec-mail ext /usr/lib/dovecot/expire-tool --test
Error: userdb(user1 at mail.example) didn't return a home directory
Info: User lookup failed: user1 at mail.example
Error: userdb(user2 at mail.example) didn't return a home directory
Info: User lookup failed: user2 at mail.example
-------------------------

Yet these mailboxes are valid, corresponding users can login, send and 
receive mail. Other mailboxes are OK, too.
Where to to start looking? I found that similar error message with 
v1.1.6 is fixed in v1.1.7, but I am running v.1.1.7 already.
Please see dovecot configuration below.
Thank you for your time,
Ivars

# 1.1.7: /etc/dovecot/dovecot.conf
# OS: Linux 2.6.27-9-server i686 Ubuntu 8.10 ext3
base_dir: /var/run/dovecot/
syslog_facility: local1
protocols: imap imaps pop3 pop3s managesieve
ssl_cert_file: /etc/certs/mail.mail.example.crt
ssl_key_file: /etc/certs/mail.mail.example.key
disable_plaintext_auth: no
login_dir: /var/run/dovecot//login
login_executable(default): /usr/lib/dovecot/imap-login
login_executable(imap): /usr/lib/dovecot/imap-login
login_executable(pop3): /usr/lib/dovecot/pop3-login
login_executable(managesieve): /usr/lib/dovecot/managesieve-login
login_user: postfix
login_greeting: VDEAVK epasta serveris.
login_processes_count: 2
first_valid_uid: 107
mail_location: maildir:/home/vmail/%d/%n
mail_executable(default): /usr/lib/dovecot/imap
mail_executable(imap): /usr/lib/dovecot/imap
mail_executable(pop3): /usr/lib/dovecot/pop3
mail_executable(managesieve): /usr/lib/dovecot/managesieve
mail_plugins(default): expire fts fts_squat antispam
mail_plugins(imap): expire fts fts_squat antispam
mail_plugins(pop3): expire
mail_plugins(managesieve): 
mail_plugin_dir(default): /usr/lib/dovecot/modules/imap
mail_plugin_dir(imap): /usr/lib/dovecot/modules/imap
mail_plugin_dir(pop3): /usr/lib/dovecot/modules/pop3
mail_plugin_dir(managesieve): /usr/lib/dovecot/modules/managesieve
managesieve_implementation_string(default): dovecot
managesieve_implementation_string(imap): dovecot
managesieve_implementation_string(pop3): dovecot
managesieve_implementation_string(managesieve): Cyrus timsieved v2.2.13
sieve_storage(default): 
sieve_storage(imap): 
sieve_storage(pop3): 
sieve_storage(managesieve): /etc/dovecot/sieve/
sieve(default): 
sieve(imap): 
sieve(pop3): 
sieve(managesieve): /home/vmail/sieve-scripts/%u.sieve
auth default:
  mechanisms: PLAIN LOGIN
  user: vmail
  username_format: %n at mail.example
  verbose: yes
  passdb:
    driver: sql
    args: /etc/dovecot/dovecot-mysql.conf
  userdb:
    driver: sql
    args: /etc/dovecot/dovecot-mysql.conf
  socket:
    type: listen
    client:
      path: /var/spool/postfix/private/auth
      mode: 432
      user: postfix
      group: postfix
    master:
      path: /var/run/dovecot/auth-master
      mode: 384
      user: vmail
      group: vmail
plugin:
  sieve: /home/vmail/sieve-scripts/%u.sieve
  expire: Trash 30 Trash/* 30 Spam 60
  expire_dict: proxy::expire
  fts: squat
  antispam_signature: X-DSPAM-Signature
  antispam_trash: trash;Trash;Deleted Items
  antispam_spam: Spam
  antispam_dspam_binary: /usr/bin/dspam
  antispam_dspam_args: --deliver=;--user;%u;-s
  antispam_mail_tmpdir: /tmp
  antispam_mail_sendmail: /usr/sbin/sendmail
  antispam_mail_spam: spam-%u at mail.example
  antispam_mail_notspam: notspam-%u at mail.example
  antispam_crm_binary: /bin/false
dict:
  expire: mysql:/etc/dovecot/dovecot-dict-expire.conf

root at mail:~# cat /etc/dovecot/dovecot-dict-expire.conf 
connect = host=127.0.0.1 dbname=postfix user=postfix password=removed
table = expire
select_field = timestamp
where_field = path
username_field = username
root at mail:~# 

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