what do i need sieve for ?

Hi,
on SuSE 9.1 Linux i use postfix 2.0.19 with cyrus_imap. to ask about sieve I
was forced by the follwing error:

Apr 11 10:44:42 orion lmtpunix[27150]: accepted connection
Apr 11 10:44:42 orion lmtpunix[27150]: lmtp connection preauth'd as postman
Apr 11 10:44:42 orion master[29103]: about to exec /usr/lib/cyrus/bin/lmtpd
Apr 11 10:44:42 orion lmtpunix[29103]: executed
Apr 11 10:44:42 orion lmtpunix[27150]: sieve runtime error for zbyszek id
<002a01c5382b$90c3d6f0$0c00000a@Ewelina>: Run error
Apr 11 10:44:42 orion lmtpunix[27150]: duplicate_check:
<002a01c5382b$90c3d6f0$0c00000a@Ewelina> user.zbyszek*********0
Apr 11 10:44:42 orion lmtpunix[27150]: mystore: starting txn 2147483728
Apr 11 10:44:42 orion lmtpunix[27150]: mystore: committing txn 2147483728
Apr 11 10:44:42 orion lmtpunix[27150]: duplicate_mark:
<002a01c5382b$90c3d6f0$0c00000a@Ewelina> user.zbyszek*********1113209082
13302
Apr 11 10:44:42 orion postfix/lmtp[29102]: C312456838:
to=<zbyszek@evot.org>,
relay=/var/spool/postfix/public/lmtp[/var/spool/postfix/public/lmtp],
delay=1, status=sent (250 2.1.5 Ok)


each mail i receive seems to pass this error. I have ony a view mailboxex.
I'll probably never use my own sieve scripts. Cann i switch it completely
off, or it's jest a neccessary component of postfix - cyrus_imap
communication ? What is the cause of this error ?

thanx in advance,
********zbyszek
--
http://zbyszek.evot.org