# dovecot -n

==> see attachment

# grep -B2 -A1 'mail_plugins =' /etc/dovecot/conf.d/*

/etc/dovecot/conf.d/10-mail.conf-#auth_socket_path = /var/run/dovecot/auth-userdb
/etc/dovecot/conf.d/10-mail.conf-#mail_plugin_dir = /usr/lib/dovecot/modules
/etc/dovecot/conf.d/10-mail.conf:#mail_plugins =
/etc/dovecot/conf.d/10-mail.conf-#mailbox_list_index = no
--
/etc/dovecot/conf.d/10-mail.conf.ucf-dist-# Space separated list of plugins to load for all services. Plugins specific to
/etc/dovecot/conf.d/10-mail.conf.ucf-dist-# IMAP, LDA, etc. are added to this list in their own .conf files.
/etc/dovecot/conf.d/10-mail.conf.ucf-dist:#mail_plugins =
/etc/dovecot/conf.d/10-mail.conf.ucf-dist-
--
/etc/dovecot/conf.d/13-quota.conf-}
/etc/dovecot/conf.d/13-quota.conf-
/etc/dovecot/conf.d/13-quota.conf:mail_plugins = $mail_plugins quota
/etc/dovecot/conf.d/13-quota.conf-
/etc/dovecot/conf.d/13-quota.conf-protocol imap {
/etc/dovecot/conf.d/13-quota.conf:  mail_plugins = $mail_plugins imap_quota
/etc/dovecot/conf.d/13-quota.conf-}
--
/etc/dovecot/conf.d/15-lda.conf-#lda_mailbox_autosubscribe = no
/etc/dovecot/conf.d/15-lda.conf-protocol lda {
/etc/dovecot/conf.d/15-lda.conf:  mail_plugins = $mail_plugins sieve
/etc/dovecot/conf.d/15-lda.conf-}
--
/etc/dovecot/conf.d/15-lda.conf.ucf-dist-protocol lda {
/etc/dovecot/conf.d/15-lda.conf.ucf-dist-  # Space separated list of plugins to load (default is global mail_plugins).
/etc/dovecot/conf.d/15-lda.conf.ucf-dist:  #mail_plugins = $mail_plugins
/etc/dovecot/conf.d/15-lda.conf.ucf-dist-}
--
/etc/dovecot/conf.d/20-imap.conf-#imap_urlauth_host =
/etc/dovecot/conf.d/20-imap.conf-protocol imap {
/etc/dovecot/conf.d/20-imap.conf:  #mail_plugins = $mail_plugins quota
/etc/dovecot/conf.d/20-imap.conf-  #mail_max_userip_connections = 10
--
/etc/dovecot/conf.d/20-imap.conf.ucf-dist-protocol imap {
/etc/dovecot/conf.d/20-imap.conf.ucf-dist-  # Space separated list of plugins to load (default is global mail_plugins).
/etc/dovecot/conf.d/20-imap.conf.ucf-dist:  #mail_plugins = $mail_plugins
/etc/dovecot/conf.d/20-imap.conf.ucf-dist-
--
/etc/dovecot/conf.d/20-managesieve.conf-  #managesieve_max_line_length = 65536
/etc/dovecot/conf.d/20-managesieve.conf-  #mail_max_userip_connections = 10
/etc/dovecot/conf.d/20-managesieve.conf:  #mail_plugins =
/etc/dovecot/conf.d/20-managesieve.conf-  #managesieve_logout_format = bytes=%i/%o
--
/etc/dovecot/conf.d/20-managesieve.conf.ucf-dist-  # Space separated list of plugins to load (none known to be useful so far).
/etc/dovecot/conf.d/20-managesieve.conf.ucf-dist-  # Do NOT try to load IMAP plugins here.
/etc/dovecot/conf.d/20-managesieve.conf.ucf-dist:  #mail_plugins =
/etc/dovecot/conf.d/20-managesieve.conf.ucf-dist-
--
/etc/dovecot/conf.d/20-pop3.conf-protocol pop3 {
/etc/dovecot/conf.d/20-pop3.conf-  # Space separated list of plugins to load (default is global mail_plugins).
/etc/dovecot/conf.d/20-pop3.conf:  #mail_plugins = $mail_plugins
/etc/dovecot/conf.d/20-pop3.conf-

Le 2018-05-16 21:40, Christian Kivalo a écrit :

On 2018-05-16 21:07, forums@mehl-family.fr wrote:

OK.

I renamed "conf.d/90-quota.conf" to "conf.d/13-quota.conf" and I have
no more this message.

This doesn't really fix your problem, you just removed the signs of it. The order of the files in /etc/dovecot/conf.d matters.

Please provide the following:
doveconf -n

grep -B2 -A1 'mail_plugins =' /etc/dovecot/conf.d/*` shows the unexpanded mail_plugins settings from your config.