I do not know windows outlook at all, but can you not use fetchmail to get the mail from the ISP to the linux server? Perhaps I am confused as to what you want to do, but here is how I work it for multiple users at home:
Mail to me is received at my ISP as firstname.lastname@example.org
, my home box has a host name of home, making its FQDN home.notreally.net. I have sendmail set to masquerade as notreally.net so that replies from my mail go to email@example.com
rather than firstname.lastname@example.org
, since home.notreally.net does not exist in the real world (especially as I have a dynamic IP). I use pop3 and fetchmail to get the mail from the ISP mailserver to home. For each user I have at home I have an identical user at my ISP (it is a small ISP so I pretty much have my choice of names and they allow unlimited number of usernames. Mail sent from home is delivered directly to recipients in the outside world without spooling through the ISP mail server, (i.e. with no relay host) -- this more or less in regards to another of your questions here on LQ).
Hope this helps and I am not off-base on what you are looking for.