[Dovecot] problem with some mailboxes (failed: Is a directory)

[mikie at x.org.pl]

>> I have this problem with some mailboxes (actually Maildirs) on my
>> system.
>> After some user's activity there is following information in dovecot
>> logs:
>>
>> Jan 29 16:24:28 mailserv dovecot: IMAP(username):
>> unlink(/var/spool/mail/imap/user/username/Maildir/cur/Sent:2,ST) failed:
>> Is a directory
>>
>> User can not connect to his account neither via POP3 nor IMAP.
>> There is one workaround I know which is:
>>
>> rm /var/spool/mail/imap/user/username/Maildir/dovecot.index*
>>
>> But after some time (some activity of user) the problem comes back.
>>
>>
>> Mikie
>>
> Please post the configuration of dovecot (dovecot -n) for more
> information of your problem.

# 1.0.15: /etc/dovecot/dovecot.conf
log_path: /var/log/dovecot.log
info_log_path: /var/log/dovecot-info.log
log_timestamp: %Y-%m-%d %H:%M:%S
protocols: imap imaps pop3 pop3s
ssl_cert_file: /etc/apache2/ssl/server.crt
ssl_key_file: /etc/apache2/ssl/server.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
first_valid_uid: 100
first_valid_gid: 100
default_mail_env: maildir:%h
mail_location: maildir:%h
mail_debug: yes
mail_executable(default): /usr/lib/dovecot/imap
mail_executable(imap): /usr/lib/dovecot/imap
mail_executable(pop3): /usr/lib/dovecot/pop3
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
pop3_uidl_format(default):
pop3_uidl_format(imap):
pop3_uidl_format(pop3): %f
auth default_with_listener:
 mechanisms: plain login
 verbose: yes
 passdb:
   driver: sql
   args: /etc/dovecot/dovecot-sql.conf
 userdb:
   driver: sql
   args: /etc/dovecot/dovecot-sql.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: mailsystem
auth default:
 user: mailsystem
 verbose: yes
 passdb:
   driver: sql
   args: /etc/dovecot/dovecot-sql.conf
 userdb:
   driver: sql
   args: /etc/dovecot/dovecot-sql.conf