You need to have a static IP and an mx record and a domain all pointing to that computer which has to be accessible from the net (ie holes in a firewall/router for ports 110, 25 at minimum). Your ISP really has nothing to do with that unless you are talking about porting over an already existing email address. Like bob@myisp.com In which case odds are they won't because that's their own domain. You would need to create your own email address bob@mydomain.com and register all of that.
Outgoing email is actually easier. You just have to enable it on your exchange server and then use it as your outbound email server. However unless it's responding correctly and reachable and looks like a legitimate server then there is a good chance that any email you send through it will look like a redirected email and get bounced.
Sooooo what is it you are actually trying to do? Are you setting this up for a real company with a real server with an owned domain or did you get a copy of exchange somehow and you are throwing it together in your basement because it looks like fun?
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Outgoing email is actually easier. You just have to enable it on your exchange server and then use it as your outbound email server. However unless it's responding correctly and reachable and looks like a legitimate server then there is a good chance that any email you send through it will look like a redirected email and get bounced.
Sooooo what is it you are actually trying to do? Are you setting this up for a real company with a real server with an owned domain or did you get a copy of exchange somehow and you are throwing it together in your basement because it looks like fun?