[Dovecot] Bounce messages

[Thanh Long DANG]

Hi,
I just set up my mail server using postfix / dovecot / mysql and it works well. I just have a problem : I'm a trying to have a overquota notification and the server sends nothing (mail server rejects incoming mail).
Could you tell me if there is a problem with dovecot or postfix configuration?
Kind regards,Long
My conf :
# 2.1.7: /etc/dovecot/dovecot.conf# OS: Linux 2.6.32-26-pve x86_64 Debian 7.2 simfsauth_mechanisms = plain logindebug_log_path = /var/log/dovecot-debug.logdict {  quotadict = mysql:/etc/dovecot/dovecot-dict-sql.conf}disable_plaintext_auth = noinfo_log_path = /var/log/dovecot-info.loglog_path = /var/log/dovecot.logmail_location = maildir:/home/vmail/%d/%n:INDEX=/home/vmail/%d/%n/indexesnamespace 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 =}passdb {  args = /etc/dovecot/dovecot-mysql.conf.ext  driver = sql}plugin {  quota = maildir:User quota  quota_exceeded_message = Storage quota for this account has been exceeded, please try again later.  quota_rule = *:storage=1G  quota_rule2 = Trash:storage=+30%%  quota_rule3 = Sent:storage=+30%%  quota_warning = storage=90%% quota-warning 90 %u  quota_warning2 = storage=75%% quota-warning 75 %u  sieve = ~/.dovecot.sieve  sieve_dir = ~/sieve}postmaster_address = postmaster at multidist.euprotocols = " imap lmtp pop3"quota_full_tempfail = yesrejection_subject = Rejet: %sservice auth {  unix_listener /var/spool/postfix/private/auth {    mode = 0666  }}service dict {  unix_listener dict {    mode = 0777  }}service lmtp {  unix_listener /var/spool/postfix/private/dovecot-lmtp {    group = postfix    mode = 0666    user = postfix  }}service quota-warning {  executable = script /usr/local/bin/quota-warning.sh  unix_listener quota-warning {    mode = 0777  }}ssl_cert = </etc/dovecot/dovecot.pemssl_key = </etc/dovecot/private/dovecot.pemuserdb {  args = /etc/dovecot/dovecot-mysql.conf.ext  driver = sql}verbose_proctitle = yesprotocol lmtp {  mail_plugins = " quota"}protocol lda {  info_log_path = /var/log/dovecot-lda.log  log_path = /var/log/dovecot-lda-errors.log  mail_plugins = " quota"}protocol imap {  mail_max_userip_connections = 10  mail_plugins = quota imap_quota}protocol pop3 {  mail_plugins = quota  pop3_uidl_format = %08Xu%08Xv}