Changing e-mail subject lines

Dear All, One of the things I do like about outlook is the ability to change the subject lines of received e-mails. I have several clients that send me mails with subjects like: "New Inquiry", 'Old Quote' , 'New Order'. After a couple of months looking at / finding e-mails is a paign in the ass. My mail client of choice is Kmail, and as far as I see I can't do this. Does anyone have any suggestions how I could get round this either with or without kmail. Regards, Jethro