agattei wrote:no, /etc/dovecto/share-folder.conf doesn't exist.
OK, here we go.
Please backup files which we're going to modify before you actually modify it.
1) Create 3 SQL tables in database 'iredadmin': used_quota, share_folder,
anyone_share.
With OpenLDAP backend, these 3 tables are created in database 'iredadmin', but
they're in database 'vmail' with MySQL and PostgreSQL backend.
If you already have them, skip this step. If you don't have them all, or some of them, please find SQL structure templates in iRedMail-0.8.1, then create them.
samples/dovecot/used_quota.sql # <- table used_quota
samples/dovecot/imap_share_folder.sql # <- table share_folder and anyone_share
2) Make sure you have below content in dovecot.conf, nested in "plugin {}":
# ACL and share folder
acl = vfile
acl_shared_dict = proxy::acl
# By default Dovecot doesn't allow using the IMAP "anyone" or
# "authenticated" identifier, because it would be an easy way to spam
# other users in the system. If you wish to allow it,
#acl_anyone = allow
If you're not sure how it looks like, please refer to sample config file
shipped in iRedMail-0.8.1: samples/dovecot/dovecot2.conf.
3) Make sure you have below content in dovecot.conf, nested in "dict {}":
acl = mysql:/etc/dovecot/dovecot-share-folder.conf
Again, if you're not sure how it looks like, please refer to sample config file
shipped in iRedMail-0.8.1: samples/dovecot/dovecot2.conf.
4) Copy iRedMail-0.8.1/samples/dovecot/dovecot-share-folder.conf to /etc/dovecot/dovecot-share-folder.conf.
Open /etc/dovecot/dovecot-share-folder.conf, you will find some words start with
'PH_', they're placeholders which will be replaced by correct value during
iRedMail installation, you have to set correct MySQL username, database
name/password in it now.
You can find SQL related settings used in dovecot-share-folder.conf in
/etc/dovecot/used-quota.conf.
Replace 'PH_DOVECOT_SHARE_FOLDER_DB_TABLE' by 'share_folder' (without quotes).
Replace 'PH_DOVECOT_SHARE_FOLDER_ANYONE_DB_TABLE' by 'anyone_share'.
With above steps, you now have IMAP share folder related settings, but it's
disabled. To enable it, please append required plugin name in
/etc/dovecot/dovecot.conf:
protocol lda {
mail_plugins = ... acl # <-- add 'acl'
}
protocol imap {
mail_plugins = ... acl imap_acl # <- add 'acl' and 'imap_acl'
}
Restarting Dovecot service is required to reload config files.
Hope it helps. 
]]>