Hi!

About 4-6 MUA Thunderbird 60.6.1 are going to connect with dovecot 2.2.13/IMAP (debian 8) and are using the same user/password. This setup works for years flawless (updated clients and serversoftware).

Since a few weeks there is one major trouble:

I one of the client moves a mail from the inbox to a another IMAP-Folder, most of the moved mail are moved for the moment. But an unstable period later, the mails are moved back to the inbox. In rarely cases, the moved mail is copied (one in the inbox, one in the destinationfolder).

Now I have to check, if this a Thunderbird-Issue or is this a dovecot-issue. For that reason, I will activate the extended logging of dovecot.

### ### ### ###
dovecot -n
# 2.2.13: /etc/dovecot/dovecot.conf
# OS: Linux 3.16.0-6-amd64 x86_64 Debian 8.11 
auth_mechanisms = plain login
debug_log_path = /var/log/mail.dovecot-debug
disable_plaintext_auth = no
info_log_path = /var/log/mail.dovecot-info
listen = *,[::]
log_path = /var/log/mail.dovecot-error
log_timestamp = "%Y-%m-%d %H:%M:%S "
mail_debug = yes
mail_max_userip_connections = 100
mail_privileged_group = vmail
passdb {
  args = /etc/dovecot/dovecot-sql.conf
  driver = sql
}
plugin {
  mail_log_events = delete undelete expunge copy mailbox_delete mailbox_rename
  mail_log_fields = uid box msgid size
  quota = dict:user::file:/var/vmail/%d/%n/.quotausage
  sieve = /var/vmail/%d/%n/.sieve
  sieve_max_redirects = 25
}
protocols = imap pop3
service auth {
  unix_listener /var/spool/postfix/private/auth {
    group = postfix
    mode = 0660
    user = postfix
  }
  unix_listener auth-userdb {
    group = vmail
    mode = 0600
    user = vmail
  }
  user = root
}
service imap-login {
  client_limit = 1000
  process_limit = 512
}
service lmtp {
  unix_listener /var/spool/postfix/private/dovecot-lmtp {
    group = postfix
    mode = 0600
    user = postfix
  }
}
ssl_cert = </etc/postfix/smtpd.cert
ssl_key = </etc/postfix/smtpd.key
ssl_protocols = !SSLv3
userdb {
  driver = prefetch
}
userdb {
  args = /etc/dovecot/dovecot-sql.conf
  driver = sql
}
protocol imap {
  mail_plugins = quota imap_quota
}
protocol pop3 {
  mail_plugins = quota
  pop3_uidl_format = %08Xu%08Xv
}
protocol lda {
  mail_plugins = sieve quota
  postmaster_address = postmaster@monarch.products4more.at
}
protocol lmtp {
  mail_plugins = quota sieve
  postmaster_address = postmaster@monarch.products4more.at
}

### ### ### ### ### ### ### ###

It works: dovecot logs to three differnt logfiles /var/log/mail.dovecot-*
It doesnt work:

plugin {
  mail_log_events = delete undelete expunge copy mailbox_delete mailbox_rename
  mail_log_fields = uid box msgid size
}

I cant see such events in the logfiles. Which switch is to turn on to log all events?
Or do anyone know the reason for the annoying "copy/move-the-mail-back"-issue?

Thank you in advance for all inputs.

regards, martin