sieve-filter with duplicate-extension

[hendrik]

Hi,

i have imported a mailbox twice (accentially). Now i thought, it might 
be a valid approach to simply use a custom sieve rule to mark duplicates 
using the attached ruleset

I ran sieve-filter like this:

    ~# sieve-filter -e -W -v -C -u user...@example.com 
/var/vmail/example.com/userxyz/sieve/duplicates.sieve 'INBOX'


But sieve-filter complains like this:

info: msgid=<1231321313212312312...@p3enginer2.emv2.com>: left message 
in mailbox 'INBOX'.
info: message kept in source mailbox.
info: filtering: [Sun, 1 May 2011 16:41:46 +0100; 101297 bytes] `Cipo & 
Baxx, Nike Golf, Strenesse, al...'.
roundcube2: line 3: warning: duplicate test: duplicate checking not 
available in this context.
info: msgid=<1123123123123...@p3enginer3.emv2.com>: left message in 
mailbox 'INBOX'.
info: message kept in source mailbox.
info: filtering: [Sun, 28 Oct 2012 11:32:56 +0100; 1416 bytes] 
`DenyHosts Report for example.com'.
roundcube2: line 3: warning: duplicate test: duplicate checking not 
available in this context.


Is there a way, to refilter an existing mailbox and applying the 
duplicate extension?


Many thanks and best regards,
Hendrikrequire ["fileinto","imap4flags","regex","variables","vnd.dovecot.duplicate"];

if duplicate {
        addflag "duplicate";
} else {
        addflag "non-duplicate";
}