[Dovecot] Protect some mailbox to remove

[FireFly]

I've installed dovecot 0.99.14 (maildir, postfix,
RHEL3) and I would like to create , for every user, 4
mailbox (in skel): mail-sent, spam, virus-alert and
sysadm. Procmail, parsing header mail, will move mails
into a specific mailbox. Every users could move,
delete, read these mails but they must not delete
mailbox folder (such as INBOX mail).

Thanks in advance,
  Francesco

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