Thanks for the advice Aki

On 6 Aug 2018, at 07:26, Aki Tuomi <aki.tuomi@dovecot.fi> wrote:

userdb {
   driver = username_format=%Lu passwd-file
   args = /etc/dovecot/share.passwd
}

Something is wrong with the suggested driver configuration – Leads to a fatal – I think there is missing a driver name.
Any chance of doing this via LDAP attribute? 

Here is my working config (without your suggestion):
# 2.2.13: /etc/dovecot/dovecot.conf
# OS: Linux 3.16.0-6-amd64 x86_64 Debian 8.11 
auth_debug = yes
auth_debug_passwords = yes
auth_mechanisms = plain login
auth_verbose = yes
auth_verbose_passwords = plain
debug_log_path = syslog
disable_plaintext_auth = no
info_log_path = syslog
lda_mailbox_autocreate = yes
lda_mailbox_autosubscribe = yes
login_log_format_elements = user=<%u> method=%m rip=%r lip=%l mpid=%e %c
mail_debug = yes
mail_gid = 5000
mail_location = maildir:~/Maildir
mail_plugins = zlib quota acl
mail_uid = 5000
managesieve_notify_capability = mailto
managesieve_sieve_capability = fileinto reject envelope encoded-character vacation subaddress comparator-i;ascii-numeric relational regex imap4flags copy include variables body enotify environment mailbox date ihave
namespace {
  hidden = no
  ignore_on_failure = no
  inbox = no
  list = children
  location = maildir:%%h/Maildir:INDEX=%h/shared/%%u:CONTROL=%h/shared/%%u
  prefix = shared/%%u/
  separator = /
  subscriptions = yes
  type = shared
}
namespace inbox {
  inbox = yes
  location = 
  mailbox Drafts {
    auto = subscribe
    special_use = \Drafts
  }
  mailbox Sent {
    auto = subscribe
    special_use = \Sent
  }
  mailbox "Sent Messages" {
    special_use = \Sent
  }
  mailbox Spam {
    auto = subscribe
    special_use = \Junk
  }
  mailbox Trash {
    auto = subscribe
    special_use = \Trash
  }
  prefix = 
  separator = /
  type = private
}
passdb {
  args = /etc/dovecot/dovecot-ldap.conf
  driver = ldap
}
plugin {
  acl = vfile
  acl_shared_dict = file:/var/spool/postfix/virtual/shared-mailboxes
  quota = maildir:User quota
  quota_exceeded_message = 4.2.2 Mailbox full
  quota_rule = *:storage=1G
  quota_rule2 = INBOX.Trash:storage=+100M
  quota_rule3 = INBOX.Spam:ignore
  quota_warning = storage=95%% quota-warning 95 %u
  sieve = ~/.dovecot.sieve
  sieve_before = /var/lib/dovecot/sieve/default.sieve
  sieve_dir = ~/sieve
  sieve_max_actions = 32
  sieve_max_redirects = 4
  sieve_max_script_size = 1M
  sieve_quota_max_scripts = 0
  sieve_quota_max_storage = 0
}
protocols = " imap lmtp sieve pop3"
service auth {
  group = dovecot
  unix_listener /var/spool/postfix/private/auth {
    group = postfix
    mode = 0666
    user = postfix
  }
  unix_listener auth-master {
    group = vmail
    mode = 0666
    user = vmail
  }
  unix_listener auth-userdb {
    group = vmail
    mode = 0666
    user = vmail
  }
  user = dovecot
}
service lmtp {
  unix_listener lmtp {
    mode = 0666
  }
}
service managesieve-login {
  inet_listener sieve {
    port = 4190
  }
  inet_listener sieve_deprecated {
    port = 2000
  }
  process_min_avail = 0
  service_count = 1
  vsz_limit = 64 M
}
ssl = no
userdb {
  args = /etc/dovecot/dovecot-ldap.conf
  driver = ldap
}
protocol lmtp {
  mail_plugins = zlib quota acl sieve
}
protocol lda {
  auth_socket_path = /var/run/dovecot/auth-master
  deliver_log_format = msgid=%m: %$
  mail_plugins = zlib quota acl sieve
  postmaster_address = postmaster@onnet.ch
}
protocol imap {
  mail_plugins = zlib quota acl imap_quota imap_acl
}
protocol sieve {
  info_log_path = /var/log/sieve.log
  log_path = /var/log/sieve.log
  mail_max_userip_connections = 10
  managesieve_implementation_string = Dovecot Pigeonhole
  managesieve_logout_format = bytes=%i/%o
  managesieve_max_compile_errors = 5
  managesieve_max_line_length = 65536
}

Thanks in advance for your help