Question about Outlook Express

I didn't know why my emails were going to outlook AND the free webmail from my service provider (optus).  After many calls between microsoft and optus I was told that my email should be POP.  Optus have all webmail set to pop but the outlook is IMAP.  Microsoft cannot help because they said it was not in waranty agreement???? The problem is that I have a very limited capacity with free optus webmail and because what happens in one happens in the other, including deleting, so my outlook is so limited it's next to usless.  I have very limited computer skills and cannot do this alone. Please help