Hi,

I'm new on this mailing list and I'm struggling with the configuration of shared mailboxes.

I've followed the following documentation page : https://doc.dovecot.org/configuration_manual/shared_mailboxes/shared_mailboxes/ and manage to had it working for something like 2 minutes, but then changed a parameter and can't get it back working (and of course I don't remember which one it was).

I'm using dovecot 2.3.13 .

user@hostname:~# dovecot -n
# 2.3.13 (89f716dc2): /etc/dovecot/dovecot.conf
# Pigeonhole version 0.5.13 (cdd19fe3)
# OS: Linux 5.10.0-19-amd64 x86_64 Debian 11.5
# Hostname: hostname
auth_mechanisms = plain login
dict {
  acl = mysql:/etc/dovecot/dovecot-dict-sql.conf.ext
}
mail_debug = yes
mail_home = /var/vmail/%d/%n
mail_location = maildir:~/
mail_plugins = acl
mail_privileged_group = mail
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 index ihave duplicate mime foreverypart extracttext
namespace {
  list = yes
  location = maildir:/var/mail/vmail/%%d/%%n/Maildir:INDEXPVT=/var/mail/vmail/%%d/%%n/Maildir/shared/%n
  prefix = shared/%%u/
  separator = /
  subscriptions = no
  type = shared
}
namespace inbox {
  inbox = yes
  location =
  mailbox Drafts {
    special_use = \Drafts
  }
  mailbox Junk {
    special_use = \Junk
  }
  mailbox Sent {
    special_use = \Sent
  }
  mailbox "Sent Messages" {
    special_use = \Sent
  }
  mailbox Trash {
    special_use = \Trash
  }
  prefix =
  separator = /
  type = private
}
passdb {
  args = /etc/dovecot/dovecot-sql.conf.ext
  driver = sql
}
plugin {
  acl = vfile
  acl_shared_dict = proxy::acl
  sieve = file:~/sieve;active=~/.dovecot.sieve
}
protocols = " imap sieve"
service auth {
  unix_listener /var/spool/postfix/private/auth {
    group = postfix
    mode = 0660
    user = postfix
  }
  unix_listener auth-userdb {
    mode = 0600
    user = vmail
  }
  user = dovecot
}
ssl_cert = </etc/letsencrypt/live/domain/fullchain.pem
ssl_client_ca_dir = /etc/ssl/certs
ssl_dh = # hidden, use -P to show it
ssl_key = # hidden, use -P to show it
userdb {
  args = uid=vmail gid=vmail home=/var/mail/vmail/%d/%n
  driver = static
}
protocol imap {
  mail_plugins = acl imap_acl imap_acl
}
protocol lda {
  mail_plugins = acl sieve
}

This is the content of dovecot-dict-sql.conf.ext :

cat dovecot-dict-sql.conf.ext
# This file is commonly accessed via dict {} section in dovecot.conf

connect = host=localhost dbname=my_dbname user=my_admin_db_user password=my_password

map {
  pattern = shared/shared-boxes/user/$to/$from
  table = user_shares
  value_field = dummy

  fields {
    from_user = $from
    to_user = $to
  }
}

map {
  pattern = shared/shared-boxes/anyone/$from
  table = anyone_shares
  value_field = dummy

  fields {
    from_user = $from
  }
}

Now, I have configured some rigth through SOGo interface as I need to use it.

With doveadm I can see the good rights :

doveadm acl get -u user1@domain INBOX
ID                                    Global Rights                                                                                                                                                                                                          
user=user2@devops.algoo.net         lookup read                                                                                                                                                                                                     
user=user3@devops.algoo.net        admin create delete expunge insert lookup post read write write-deleted write-seen                                                                                                                              

This this the output I have from journalctl -f command with debug enabled when trying to access to the shared folder within SOGo :

Nov 15 17:51:14 hostname dovecot[269267]: imap-login: Login: user=<user3@domain>, method=PLAIN, rip=127.0.0.1, lip=127.0.0.1, mpid=270025, secured, session=<UL//KYXt7ul/AAAB>
Nov 15 17:51:14 hostname dovecot[269267]: imap(user3user3@domain)<270025><UL//KYXt7ul/AAAB>: Debug: Loading modules from directory: /usr/lib/dovecot/modules
Nov 15 17:51:14 hostname dovecot[269267]: imap(user3@domain)<270025><UL//KYXt7ul/AAAB>: Debug: Module loaded: /usr/lib/dovecot/modules/lib01_acl_plugin.so
Nov 15 17:51:14 hostname dovecot[269267]: imap(user3@domain)<270025><UL//KYXt7ul/AAAB>: Debug: Module loaded: /usr/lib/dovecot/modules/lib02_imap_acl_plugin.so
Nov 15 17:51:14 hostname dovecot[269267]: imap(user3@domain)<270025><UL//KYXt7ul/AAAB>: Debug: Effective uid=5000, gid=5000, home=/var/mail/vmail/domain/user3
Nov 15 17:51:14 hostname dovecot[269267]: imap(user3@domain)<270025><UL//KYXt7ul/AAAB>: Debug: Namespace inbox: type=private, prefix=, sep=/, inbox=yes, hidden=no, list=yes, subscriptions=yes location=maildir:~/
Nov 15 17:51:14 hostname dovecot[269267]: imap(user3@domain)<270025><UL//KYXt7ul/AAAB>: Debug: maildir++: root=/var/mail/vmail/domain/user3, index=, indexpvt=, control=, inbox=/var/mail/vmail/domain/user3, alt=
Nov 15 17:51:14 hostname dovecot[269267]: imap(user3@domain)<270025><UL//KYXt7ul/AAAB>: Debug: acl: initializing backend with data: vfile
Nov 15 17:51:14 hostname dovecot[269267]: imap(user3@domain)<270025><UL//KYXt7ul/AAAB>: Debug: acl: acl username = user3@domain
Nov 15 17:51:14 hostname dovecot[269267]: imap(user3@domain)<270025><UL//KYXt7ul/AAAB>: Debug: acl: owner = 1
Nov 15 17:51:14 hostname dovecot[269267]: imap(user3@domain)<270025><UL//KYXt7ul/AAAB>: Debug: acl vfile: Global ACLs disabled
Nov 15 17:51:14 hostname dovecot[269267]: imap(user3@domain)<270025><UL//KYXt7ul/AAAB>: Debug: Namespace : type=shared, prefix=shared/%u/, sep=/, inbox=no, hidden=no, list=yes, subscriptions=no location=maildir:/var/mail/vmail/%d/%n/Maildir:INDEXPVT=/var/mail/vmail/%d/%n/Maildir/shared/user3
Nov 15 17:51:14 hostname dovecot[269267]: imap(user3@domain)<270025><UL//KYXt7ul/AAAB>: Debug: shared: root=/run/dovecot, index=, indexpvt=, control=, inbox=, alt=
Nov 15 17:51:14 hostname dovecot[269267]: imap(user3@domain)<270025><UL//KYXt7ul/AAAB>: Debug: acl: initializing backend with data: vfile
Nov 15 17:51:14 hostname dovecot[269267]: imap(user3@domain)<270025><UL//KYXt7ul/AAAB>: Debug: acl: acl username = user3@domain
Nov 15 17:51:14 hostname dovecot[269267]: imap(user3@domain)<270025><UL//KYXt7ul/AAAB>: Debug: acl: owner = 0
Nov 15 17:51:14 hostname dovecot[269267]: imap(user3@domain)<270025><UL//KYXt7ul/AAAB>: Debug: acl vfile: Global ACLs disabled
Nov 15 17:51:14 hostname dovecot[269267]: imap(user3@domain)<270025><UL//KYXt7ul/AAAB>: Debug: Mailbox INBOX/folder_i_want_to_share_from_user1_to_user3: Mailbox opened because: SELECT
Nov 15 17:51:14 hostname dovecot[269267]: imap(user3@domain)<270025><UL//KYXt7ul/AAAB>: Debug: acl vfile: reading file /var/mail/vmail/domain/user3/.INBOX.folder_i_want_to_share_from_user1_to_user3/dovecot-acl
Nov 15 17:51:14 hostname dovecot[269267]: imap(user3@domain)<270025><UL//KYXt7ul/AAAB>: Logged out in=140 out=1521 deleted=0 expunged=0 trashed=0 hdr_count=0 hdr_bytes=0 body_count=0 body_bytes=0
Nov 15 17:51:15 hostname dovecot[269267]: imap-login: Login: user=<user3@domain>, method=PLAIN, rip=127.0.0.1, lip=127.0.0.1, mpid=270028, secured, session=<IDgGKoXt/Ol/AAAB>
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270028><IDgGKoXt/Ol/AAAB>: Debug: Loading modules from directory: /usr/lib/dovecot/modules
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270028><IDgGKoXt/Ol/AAAB>: Debug: Module loaded: /usr/lib/dovecot/modules/lib01_acl_plugin.so
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270028><IDgGKoXt/Ol/AAAB>: Debug: Module loaded: /usr/lib/dovecot/modules/lib02_imap_acl_plugin.so
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270028><IDgGKoXt/Ol/AAAB>: Debug: Effective uid=5000, gid=5000, home=/var/mail/vmail/domain/user3
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270028><IDgGKoXt/Ol/AAAB>: Debug: Namespace inbox: type=private, prefix=, sep=/, inbox=yes, hidden=no, list=yes, subscriptions=yes location=maildir:~/
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270028><IDgGKoXt/Ol/AAAB>: Debug: maildir++: root=/var/mail/vmail/domain/user3, index=, indexpvt=, control=, inbox=/var/mail/vmail/domain/user3, alt=
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270028><IDgGKoXt/Ol/AAAB>: Debug: acl: initializing backend with data: vfile
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270028><IDgGKoXt/Ol/AAAB>: Debug: acl: acl username = user3@domain
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270028><IDgGKoXt/Ol/AAAB>: Debug: acl: owner = 1
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270028><IDgGKoXt/Ol/AAAB>: Debug: acl vfile: Global ACLs disabled
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270028><IDgGKoXt/Ol/AAAB>: Debug: Namespace : type=shared, prefix=shared/%u/, sep=/, inbox=no, hidden=no, list=yes, subscriptions=no location=maildir:/var/mail/vmail/%d/%n/Maildir:INDEXPVT=/var/mail/vmail/%d/%n/Maildir/shared/user3
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270028><IDgGKoXt/Ol/AAAB>: Debug: shared: root=/run/dovecot, index=, indexpvt=, control=, inbox=, alt=
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270028><IDgGKoXt/Ol/AAAB>: Debug: acl: initializing backend with data: vfile
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270028><IDgGKoXt/Ol/AAAB>: Debug: acl: acl username = user3@domain
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270028><IDgGKoXt/Ol/AAAB>: Debug: acl: owner = 0
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270028><IDgGKoXt/Ol/AAAB>: Debug: acl vfile: Global ACLs disabled
Nov 15 17:51:15 hostname dovecot[269267]: imap-login: Login: user=<user3@domain>, method=PLAIN, rip=127.0.0.1, lip=127.0.0.1, mpid=270029, secured, session=<7mIGKoXtAOp/AAAB>
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Debug: Loading modules from directory: /usr/lib/dovecot/modules
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Debug: Module loaded: /usr/lib/dovecot/modules/lib01_acl_plugin.so
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Debug: Module loaded: /usr/lib/dovecot/modules/lib02_imap_acl_plugin.so
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Debug: Effective uid=5000, gid=5000, home=/var/mail/vmail/domain/user3
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Debug: Namespace inbox: type=private, prefix=, sep=/, inbox=yes, hidden=no, list=yes, subscriptions=yes location=maildir:~/
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Debug: maildir++: root=/var/mail/vmail/domain/user3, index=, indexpvt=, control=, inbox=/var/mail/vmail/domain/user3, alt=
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Debug: acl: initializing backend with data: vfile
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Debug: acl: acl username = user3@domain
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Debug: acl: owner = 1
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Debug: acl vfile: Global ACLs disabled
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Debug: Namespace : type=shared, prefix=shared/%u/, sep=/, inbox=no, hidden=no, list=yes, subscriptions=no location=maildir:/var/mail/vmail/%d/%n/Maildir:INDEXPVT=/var/mail/vmail/%d/%n/Maildir/shared/user3
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Debug: shared: root=/run/dovecot, index=, indexpvt=, control=, inbox=, alt=
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Debug: acl: initializing backend with data: vfile
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Debug: acl: acl username = user3@domain
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Debug: acl: owner = 0
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Debug: acl vfile: Global ACLs disabled
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Debug: acl vfile: file /var/mail/vmail/domain/user3/dovecot-acl not found
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Debug: acl vfile: reading file /var/mail/vmail/domain/user3/.INBOX.folder_i_want_to_share_from_user1_to_user3/dovecot-acl
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270028><IDgGKoXt/Ol/AAAB>: Debug: Mailbox INBOX: Mailbox opened because: SELECT
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270028><IDgGKoXt/Ol/AAAB>: Debug: acl vfile: file /var/mail/vmail/domain/user3/dovecot-acl not found
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Debug: maildir++: root=/var/mail/vmail/domain/user1/Maildir, index=, indexpvt=/var/mail/vmail/domain/user1/Maildir/shared/user3, control=, inbox=/var/mail/vmail/domain/user1/Maildir, alt=
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Debug: acl: initializing backend with data: vfile
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Debug: acl: acl username = user1@domain
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Debug: acl: owner = 1
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Debug: acl vfile: Global ACLs disabled
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Debug: maildir++: root=/var/mail/vmail/domain/user1/Maildir, index=, indexpvt=/var/mail/vmail/domain/user1/Maildir/shared/user3, control=, inbox=/var/mail/vmail/domain/user1/Maildir, alt=
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Debug: acl: initializing backend with data: vfile
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Debug: acl: acl username = user3@domain
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Debug: acl: owner = 0
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Debug: acl vfile: Global ACLs disabled
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Debug: acl: Mailbox not in dovecot-acl-list: shared/user1@domain
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Debug: acl vfile: file /var/mail/vmail/domain/user1/Maildir/dovecot-acl not found
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Debug: Namespace shared/: Using permissions from : mode=0700 gid=default
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270028><IDgGKoXt/Ol/AAAB>: Logged out in=198 out=1581 deleted=0 expunged=0 trashed=0 hdr_count=0 hdr_bytes=0 body_count=0 body_bytes=0
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270029><7mIGKoXtAOp/AAAB>: Logged out in=125 out=1417 deleted=0 expunged=0 trashed=0 hdr_count=0 hdr_bytes=0 body_count=0 body_bytes=0
Nov 15 17:51:15 hostname dovecot[269267]: imap-login: Login: user=<user3@domain>, method=PLAIN, rip=127.0.0.1, lip=127.0.0.1, mpid=270033, secured, session=<B4gIKoXtDOp/AAAB>
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270033><B4gIKoXtDOp/AAAB>: Debug: Loading modules from directory: /usr/lib/dovecot/modules
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270033><B4gIKoXtDOp/AAAB>: Debug: Module loaded: /usr/lib/dovecot/modules/lib01_acl_plugin.so
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270033><B4gIKoXtDOp/AAAB>: Debug: Module loaded: /usr/lib/dovecot/modules/lib02_imap_acl_plugin.so
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270033><B4gIKoXtDOp/AAAB>: Debug: Effective uid=5000, gid=5000, home=/var/mail/vmail/domain/user3
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270033><B4gIKoXtDOp/AAAB>: Debug: Namespace inbox: type=private, prefix=, sep=/, inbox=yes, hidden=no, list=yes, subscriptions=yes location=maildir:~/
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270033><B4gIKoXtDOp/AAAB>: Debug: maildir++: root=/var/mail/vmail/domain/user3, index=, indexpvt=, control=, inbox=/var/mail/vmail/domain/user3, alt=
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270033><B4gIKoXtDOp/AAAB>: Debug: acl: initializing backend with data: vfile
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270033><B4gIKoXtDOp/AAAB>: Debug: acl: acl username = user3@domain
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270033><B4gIKoXtDOp/AAAB>: Debug: acl: owner = 1
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270033><B4gIKoXtDOp/AAAB>: Debug: acl vfile: Global ACLs disabled
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270033><B4gIKoXtDOp/AAAB>: Debug: Namespace : type=shared, prefix=shared/%u/, sep=/, inbox=no, hidden=no, list=yes, subscriptions=no location=maildir:/var/mail/vmail/%d/%n/Maildir:INDEXPVT=/var/mail/vmail/%d/%n/Maildir/shared/user3
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270033><B4gIKoXtDOp/AAAB>: Debug: shared: root=/run/dovecot, index=, indexpvt=, control=, inbox=, alt=
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270033><B4gIKoXtDOp/AAAB>: Debug: acl: initializing backend with data: vfile
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270033><B4gIKoXtDOp/AAAB>: Debug: acl: acl username = user3@domain
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270033><B4gIKoXtDOp/AAAB>: Debug: acl: owner = 0
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270033><B4gIKoXtDOp/AAAB>: Debug: acl vfile: Global ACLs disabled
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270033><B4gIKoXtDOp/AAAB>: Debug: Mailbox INBOX/folder_i_want_to_share_from_user1_to_user3: Mailbox opened because: SELECT
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270033><B4gIKoXtDOp/AAAB>: Debug: acl vfile: reading file /var/mail/vmail/domain/user3/.INBOX.folder_i_want_to_share_from_user1_to_user3/dovecot-acl
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270033><B4gIKoXtDOp/AAAB>: Logged out in=313 out=2117 deleted=0 expunged=0 trashed=0 hdr_count=1 hdr_bytes=2 body_count=0 body_bytes=0
Nov 15 17:51:15 hostname dovecot[269267]: imap-login: Login: user=<user3@domain>, method=PLAIN, rip=127.0.0.1, lip=127.0.0.1, mpid=270037, secured, session=<nRkMKoXtFup/AAAB>
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270037><nRkMKoXtFup/AAAB>: Debug: Loading modules from directory: /usr/lib/dovecot/modules
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270037><nRkMKoXtFup/AAAB>: Debug: Module loaded: /usr/lib/dovecot/modules/lib01_acl_plugin.so
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270037><nRkMKoXtFup/AAAB>: Debug: Module loaded: /usr/lib/dovecot/modules/lib02_imap_acl_plugin.so
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270037><nRkMKoXtFup/AAAB>: Debug: Effective uid=5000, gid=5000, home=/var/mail/vmail/domain/user3
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270037><nRkMKoXtFup/AAAB>: Debug: Namespace inbox: type=private, prefix=, sep=/, inbox=yes, hidden=no, list=yes, subscriptions=yes location=maildir:~/
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270037><nRkMKoXtFup/AAAB>: Debug: maildir++: root=/var/mail/vmail/domain/user3, index=, indexpvt=, control=, inbox=/var/mail/vmail/domain/user3, alt=
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270037><nRkMKoXtFup/AAAB>: Debug: acl: initializing backend with data: vfile
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270037><nRkMKoXtFup/AAAB>: Debug: acl: acl username = user3@domain
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270037><nRkMKoXtFup/AAAB>: Debug: acl: owner = 1
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270037><nRkMKoXtFup/AAAB>: Debug: acl vfile: Global ACLs disabled
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270037><nRkMKoXtFup/AAAB>: Debug: Namespace : type=shared, prefix=shared/%u/, sep=/, inbox=no, hidden=no, list=yes, subscriptions=no location=maildir:/var/mail/vmail/%d/%n/Maildir:INDEXPVT=/var/mail/vmail/%d/%n/Maildir/shared/user3
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270037><nRkMKoXtFup/AAAB>: Debug: shared: root=/run/dovecot, index=, indexpvt=, control=, inbox=, alt=
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270037><nRkMKoXtFup/AAAB>: Debug: acl: initializing backend with data: vfile
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270037><nRkMKoXtFup/AAAB>: Debug: acl: acl username = user3@domain
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270037><nRkMKoXtFup/AAAB>: Debug: acl: owner = 0
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270037><nRkMKoXtFup/AAAB>: Debug: acl vfile: Global ACLs disabled
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270037><nRkMKoXtFup/AAAB>: Debug: Mailbox INBOX: Mailbox opened because: SELECT
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270037><nRkMKoXtFup/AAAB>: Debug: acl vfile: file /var/mail/vmail/domain/user3/dovecot-acl not found
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270037><nRkMKoXtFup/AAAB>: Debug: Mailbox INBOX/folder_i_want_to_share_from_user1_to_user3: Mailbox opened because: SELECT
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270037><nRkMKoXtFup/AAAB>: Debug: acl vfile: reading file /var/mail/vmail/domain/user3/.INBOX.folder_i_want_to_share_from_user1_to_user3/dovecot-acl
Nov 15 17:51:15 hostname dovecot[269267]: imap(user3@domain)<270037><nRkMKoXtFup/AAAB>: Logged out in=218 out=1925 deleted=0 expunged=0 trashed=0 hdr_count=0 hdr_bytes=0 body_count=0 body_bytes=0

I tried with thunderbird too but no folders appears neither.

Do you have any clue on which parameter do I need to change in order to get it working?

Thank you very much for any help provided.

Quiwy