No success yet.

Before (10-mail.conf)

unix_listener auth-userdb { #mode = 0666 #user = #group = }

After

grep ^auth_socket_path 10-mail.conf

auth_socket_path = /var/run/dovecot/auth-userdb

grep -A 5 'unix_listener auth-userdb' 10-master.conf

unix_listener auth-userdb { #mode = 0666 user = mail group = mail }

shared-mailboxes.db is present

ll /var/mail/mymail.domain/shared-mailboxes.db

-rw-rw---- 1 mail mail 120 apr 4 17:12 /var/mail/mymail.domain/shared-mailboxes.db

If I delete the file /var/mail/mymail.domain/shared-mailboxes.db, it will still be created

cat /var/mail/mymail.domain/shared-mailboxes.db

shared/shared-boxes/user/domainuser1/apr07@mymail.domain 1 shared/shared-boxes/user/domainuser1/domainuser2@mymail.domain 1

(domainuser2 share "newfolder1" for domainuser1. And apr07 share "sharefolder" for domainuser1)

ll /var/mail/mymail.domain/apr07/dovecot-acl-list

-rw------- 1 mail mail 23 apr 7 17:11 /var/mail/mymail.domain/apr07/dovecot-acl-list

cat /var/mail/mymail.domain/apr07/dovecot-acl-list

1744027894 sharefolder

cat /var/mail/mymail.domain/domainuser2/dovecot-acl-list

1744027957 newfolder1

ll /var/mail/mymail.domain/domainuser2/ | grep newfolder1

drwx--S--- 5 mail mail 4096 apr 7 17:12 .newfolder1/

ll /var/mail/mymail.domain/apr07/ | grep sharefolder

drwx--S--- 5 mail mail 4096 apr 7 17:11 .sharefolder/