i dont not understand what you mean port 25 is open, from my understanding of how ports work. if a port is open that indicates that a service is running, not that there will no restriction on the useage of that port for means of remote connection.

if you can visit https://login.passport.com or what ever msns log in page is then the useage of 443 as a remote port is not blocked.


as for using linux as a dns server i suggest using your routers NAT feature for this.