Found the problem by myself. I have 2 accounts. One pop3 and one
Internal Exchange server. My exchange server is not connected to
internet. I am just using it for intenal mail transfer.
If i configure my outlook 2007 only for pop3 then "process marked
headers" is enabled. But if i configure both pop3 and exchange server
accounts then "process marked headers" is disabled.
I was able to use this option with outlook 2003 but outlook 2007 is
not giving this option. May be this is a bug in it or Microsoft has
done it intentionally.