General :: Fetchmail - Downloading Emails From Exchange

I am using fetchmail to download e-mails from the exchange server in sendmail box Using Centos 5.4 with Sendmail. I can download mails from exchange but want to keep all mail there in Exchange server also, which option I should use to keep that mail there as well with the help of fetchmail? My config is here below , but unable to use "keep" option and getting in the logs error below.

Code:
cat /root/.fetchmailrc
set logfile "/root/fetch/fetchlog"
set postmaster "test@example.com"
set bouncemail
set no spambounce
set properties ""
set daemon 600 .....