[Dovecot] Hot to get rid of \"DON\'T DELETE THIS MESSAGE\" messages?

[foxx at freemail.gr]

I'm using Dovecot 1.0.0 (mbox) with Postfix 2.4 on my FreeBSD box, as a pop3-only server (imap is disabled). All account mailboxes are accessed using Outlook clients.

I've noticed that, whenever I'm retrieving mail with pop3, a "DON'T DELETE THIS MESSAGE" is created in mbox. Although these messages are never sent to client MUAs, I found them very annoying.

BTW I don't use (or used before) UW or Pine or any other c-client, therefore I assume it's a Dovecot issue. Previously I was using Cyrus and never had such a problem.

Any idea how this can be fixed?

FreeBSD 6.2 Release, Postfix 2.4, Dovecot 1.0.0
dovecot -n report:

base_dir: /var/run/dovecot/
protocols: pop3
listen: *
ssl_disable: yes
disable_plaintext_auth: no
login_dir: /var/run/dovecot/login
login_executable: /usr/local/libexec/dovecot/pop3-login
login_process_per_connection: no
login_processes_count: 1
login_max_processes_count: 10
verbose_proctitle: yes
first_valid_uid: 2000
last_valid_uid: 2999
first_valid_gid: 2000
last_valid_gid: 2000
mail_extra_groups: mail
mail_location: mbox:/var/empty/:INBOX=/var/mail/%u:INDEX=MEMORY
dotlock_use_excl: yes
mbox_read_locks: flock
mbox_write_locks: flock
mail_executable: /usr/local/libexec/dovecot/pop3
mail_plugin_dir: /usr/local/lib/dovecot/pop3
pop3_no_flag_updates: yes
pop3_uidl_format: %08Xu%08Xv
pop3_client_workarounds: outlook-no-nuls oe-ns-eoh
auth default:
  default_realm: domain.com
  username_format: %n
  passdb:
    driver: passwd
  userdb:
    driver: passwd
  socket:
    type: listen
    client:
      path: /var/spool/postfix/private/auth
      mode: 432
      user: postfix
      group: postfix
    master:


regards,
Athan