If you decide to use POP3 and "Leave copy on server" be aware that Outlook doesn't always do this reliably; I've seen people lose email with this over the years. Newer Outlook versions may be much more reliable; I can't say from experience.
You can implement POP to multiple computers safely with the use of multiple emailboxes and a forwarder. For instance, to duplicate the email for
brian@somewhere.com you'd create
brian2@somewhere.com and forward a copy of email messages arriving at
brian@somewhere.com to
brian2@somewhere.com. Fiddly, but there are times when this works better than IMAP.
Ultimately with IMAP all your messages reside on the server. If you get a lot of email, there's a chance you could run into space issues; and you need to consider that.
Another option I've seen people use is to forward to Gmail. You can set Gmail to reply using the forwarded mailbox (eg as
brian@somewhere.com). You can read email either via the web interface (with funky searching) or via Outlook. Don't do this if you're a Chinese dissident!
