[Dovecot] access shared mailbox results in error

[Michael Cramer]

when i try to access a shared mailbox the logfile shows me this and access
isn't possible

Jun 15 19:38:57 imap(michael at bigmichi1.de): Error: mdbox  
/srv/vmail/mail/bigmichi1.de/familie/mailboxes/INBOX/dbox-Mails:  
Invalid dbox header size: 0
Jun 15 19:38:57 imap(michael at bigmichi1.de): Warning: fscking index  
file  
/srv/vmail/indexes/shared/bigmichi1.de/michael/shared/familie at bigmichi1.de/storage/dovecot.map.index
Jun 15 19:38:57 imap(michael at bigmichi1.de): Warning: mdbox  
/srv/vmail/mail/bigmichi1.de/familie/storage: rebuilding indexes


doveconf -n

# 2.2.2 (30f00db1a8b0): /etc/dovecot/dovecot.conf
# OS: Linux 3.8.0-25-generic x86_64 Ubuntu 13.04 ext4
auth_mechanisms = plain login
debug_log_path = /var/log/dovecot/debug.log
dict {
   acl = pgsql:/etc/dovecot/dovecot-dict-sql.conf.ext
   expire = pgsql:/etc/dovecot/dovecot-dict-sql.conf.ext
   quota = pgsql:/etc/dovecot/dovecot-dict-sql.conf.ext
}
first_valid_gid = 8
first_valid_uid = 8
info_log_path = /var/log/dovecot/info.log
last_valid_gid = 8
last_valid_uid = 8
log_path = /var/log/dovecot/error.log
mail_debug = yes
mail_gid = 8
mail_location =  
mdbox:/srv/vmail/mail/%d/%n:INDEXPVT=/srv/vmail/indexes/private/%d/%n:INDEX=/srv/vmail/indexes/shared/%d/%n
mail_plugins = quota zlib acl expire virtual
mail_uid = 8
mailbox_list_index = yes
managesieve_notify_capability = mailto
managesieve_sieve_capability = fileinto reject envelope  
encoded-character vacation subaddress comparator-i;ascii-numeric  
relational regex imap4flags copy include variab
les body enotify environment mailbox date ihave imapflags notify
mdbox_preallocate_space = yes
mdbox_rotate_size = 10 M
namespace {
   list = children
   location =  
mdbox:/srv/vmail/mail/%%d/%%n:INDEXPVT=/srv/vmail/indexes/private/%d/%n/shared/%%u:INDEX=/srv/vmail/indexes/shared/%d/%n/shared/%%u
   prefix = Shared/%%u/
   separator = /
   subscriptions = no
   type = shared
}
namespace inbox {
   inbox = yes
   location =
   mailbox Archive {
     auto = subscribe
     special_use = \Archive
   }
   mailbox Drafts {
     auto = subscribe
     special_use = \Drafts
   }
   mailbox Sent {
     auto = subscribe
     special_use = \Sent
   }
   mailbox Spam {
     auto = subscribe
     special_use = \Junk
   }
   mailbox Trash {
     auto = subscribe
     special_use = \Trash
   }
   mailbox virtual/All {
     auto = subscribe
     special_use = \All
   }
   mailbox virtual/Flagged {
     auto = subscribe
     special_use = \Flagged
   }
   prefix =
   separator = /
   type = private
}
namespace virtual {
   location =  
virtual:/srv/vmail/virtual:INDEXPVT=/srv/vmail/indexes/private/%d/%n/virtual:INDEX=/srv/vmail/indexes/shared/%d/%n/virtual
   prefix = virtual/
   separator = /
}
passdb {
   args = /etc/dovecot/dovecot-sql.conf.ext
   driver = sql
}
plugin {
   acl = vfile:/srv/vmail/acl:cache_secs=300
   acl_anyone = allow
   acl_shared_dict = proxy::acl
   expire = Trash 7 Trash/* 7 Spam 30
   expire_dict = proxy::expire
   quota = dict:User quota::proxy::quota
   quota_warning = storage=95%% quota-warning 95 %u
   quota_warning2 = storage=80%% quota-warning 80 %u
   quota_warning3 = -storage=100%% quota-warning below %u
   sieve = /srv/vmail/sieve/%d/%n/.dovecot.sieve
   sieve_default = /srv/vmail/sieve/default.sieve
   sieve_dir = /srv/vmail/sieve/%d/%n/
   sieve_extensions = +notify +imapflags
   sieve_global_dir = /srv/vmail/sieve/global
}
postmaster_address = postmaster at bigmichi1.de
protocols = " imap sieve"
service auth-worker {
   user = $default_internal_user
}
service auth {
   unix_listener /var/spool/postfix/private/auth {
     group = postfix
     mode = 0666
     user = postfix
   }
   unix_listener auth-userdb {
     group = mail
     mode = 0666
     user = mail
   }
}
service dict {
   unix_listener dict {
     group = mail
     mode = 0660
     user = mail
   }
}
service managesieve-login {
   inet_listener sieve {
     port = 4190
   }
}
service quota-warning {
   executable = script /usr/local/bin/quota-warning.sh
   unix_listener quota-warning {
     user = mail
   }
   user = dovecot
}
ssl_cert = </srv/ssl/ssl-unified.crt
ssl_key = </srv/ssl/ssl-decrypted.key
userdb {
   args = /etc/dovecot/dovecot-sql.conf.ext
   driver = sql
}
protocol lda {
   debug_log_path = /var/log/dovecot/deliver-debug.log
   info_log_path = /var/log/dovecot/deliver-info.log
   log_path = /var/log/dovecot/deliver-errors.log
   mail_plugins = quota zlib acl expire virtual sieve
}
protocol imap {
   mail_plugins = quota zlib acl expire virtual imap_quota imap_acl imap_zlib
}