If you are using an internet mail account through an ISP, do this on your main computer in either Outlook or Outlook Express:
Tools -> Accounts -> Properties -> Advanced Tab and check "Leave a copy of message on server". If you check internet mail through another computer I suggest you do the same procedure before you download your mail. Try NOT to use the wizard in Outlook Express when setting this up on a computer other than your own as the mail will down load and not save on the server. Most ISPs allow mail to be saved on the server for a length of time.