Hi,
I am just running Dovecot v 2.3.8 .. seems to work fine.
I just add the quota plugin.. and.. I cannot see any differences..  I cannot see any information on Quota per user.. No specific info on Log file  :-(

Any help please ?

Tahnks for your help

Here is my config :

# 2.3.8 (9df20d2db): /etc/dovecot/dovecot.conf
# Pigeonhole version 0.5.8 (b7b03ba2)
# OS: Linux 4.18.0-305.12.1.el8_4.x86_64 x86_64 CentOS Linux release 8.4.2105 nfs4
# Hostname: mbox1.intranet.office.itx
auth_cache_negative_ttl = 5 mins
auth_cache_ttl = 5 mins
auth_mechanisms = plain login
auth_username_format = %u
debug_log_path = /var/log/dovecot-debug.log
default_vsz_limit = 4 G
info_log_path = /var/log/dovecot-info.log
listen = * [::]
log_path = /var/log/dovecot.log
login_trusted_networks = 172.18.0.0/16 127.0.0.1 ::1
mail_access_groups = dovecot
mail_fsync = always
mail_location = maildir:/var/spool2/mail/%u:LAYOUT=fs
mail_nfs_storage = yes
mail_plugins = " quota"
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 ihave
mbox_very_dirty_syncs = yes
mbox_write_locks = fcntl
mmap_disable = yes
namespace inbox {
  disabled = no
  ignore_on_failure = no
  inbox = yes
  list = yes
  location = 
  mailbox Archive {
    auto = no
    comment = " All my Accepted/NON  SPAM"
    special_use = \Archive
  }
  mailbox Drafts {
    auto = subscribe
    special_use = \Drafts
  }
  mailbox Junk {
    auto = subscribe
    autoexpunge = 90 days
    special_use = \Junk
  }
  mailbox Sent {
    auto = subscribe
    special_use = \Sent
  }
  mailbox Trash {
    auto = no
    autoexpunge = 60 days
    special_use = \Trash
  }
  mailbox virtual/All {
    auto = no
    special_use = \All
  }
  prefix = 
  subscriptions = yes
  type = private
}
passdb {
  driver = pam
}
plugin {
  quota_grace = 10%%
  quota_max_mail_size = 100M
  quota_rule = *:storage=10000M
  quota_rule2 = Trash:Storage=+100M
  quota_rule3 = Spam:storage=+20%%
  quota_status_nouser = DUNNO
  quota_status_overquota = 552 5.2.2 Mailbox is full
  quota_status_success = DUNNO
  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 = file:~/sieve;active=~/.dovecot.sieve
}
pop3_uidl_format = %v-%u
service auth {
  unix_listener auth-master {
    mode = 0666
  }
  unix_listener auth-userdb {
    mode = 0600
    user = mail
  }
}
service dict {
  unix_listener dict {
    mode = 0600
    user = mail
  }
}
service imap-login {
  inet_listener imap {
    port = 143
  }
  inet_listener imaps {
    port = 993
    ssl = yes
  }
  process_min_avail = 4
  service_count = 0
}
service lmtp {
  inet_listener lmtp {
    port = 24
  }
  unix_listener /var/run/lmtp {
    group = mail
    mode = 0660
    user = mail
  }
}
service pop3-login {
  inet_listener pop3 {
    address = *
    port = 110
  }
  inet_listener pop3s {
    port = 995
    ssl = yes
  }
}
service quota-warning {
  executable = script /usr/local/bin/quota-warning.sh
  unix_listener quota-warning {
    user = mail
  }
  user = dovecot
}
service submission {
  process_limit = 250
}
ssl = required
ssl_ca = </etc/mail/ssl/ssl1/xxxxxp_net.ca-bundle
ssl_cert = </etc/mail/ssl/ssl1/xxxxxx_net.crt
ssl_cipher_list = HIGH:!aNULL:!ADH:!DH:!RC4:!MD5:!RSA
ssl_dh = # hidden, use -P to show it
ssl_key = # hidden, use -P to show it
userdb {
  driver = passwd
}
verbose_proctitle = yes
protocol lmtp {
  mail_fsync = optimized
  mail_plugins = autocreate quota acl fts fts_solr zlib mail_log notify sieve
  postmaster_address = it@intranet.office.itx
}
protocol lda {
  mail_fsync = optimized
  mail_plugins = " quota sieve quota"
}
protocol imap {
  mail_max_userip_connections = 80
  mail_plugins = " quota quota imap_quota"
  ssl_cert = </etc/mail/ssl/ssl1/STAR_aztgrp_net.crt
  ssl_key = # hidden, use -P to show it
}
protocol pop3 {
  mail_max_userip_connections = 10
  mail_plugins = " quota"
}
protocol submission {
  mail_max_userip_connections = 10
  mail_plugins = " quota"
}