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

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

Error: userdb(user1@mail.example) didn't return a home directory Error: userdb(user2@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@mail.example) didn't return a home directory Info: User lookup failed: user1@mail.example Error: userdb(user2@mail.example) didn't return a home directory Info: User lookup failed: user2@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 attached. Thank you for your time, Ivars