Creating folders for non users

[Nikos Gatsis]

Hello list.
I have a strange problem, with cyrus.
If system receive a message for a non existing user, cyrus creating this 
user and folders inbox,send etc.

I use sendmail-8.14.2-1.fc8 and cyrus-imapd-2.3.9-7.fc8.

My imapd.conf is:

configdirectory: /var/lib/imap
partition-default: /var/spool/imap
admins: cyrus admin
allowanonymouslogin: no
allowplaintext: yes
anyoneuseracl: 0
autocreatequota: 20480
quotawarn: 90
createonpost: yes
autocreateinboxfolders: Sent|Drafts|Trash
maxmessagesize: 7168000
sievedir: /var/lib/imap/sieve
sendmail: /usr/sbin/sendmail
hashimapspool: true
sasl_pwcheck_method: saslauthd
sasl_mech_list: PLAIN
tls_cert_file: /etc/pki/cyrus-imapd/cyrus-imapd.pem
tls_key_file: /etc/pki/cyrus-imapd/cyrus-imapd.pem
tls_ca_file: /etc/pki/tls/certs/ca-bundle.crt


How can I stop this?

Thank you, Nikos