trying to run an smtp server from a range of addresses making up homes (that is, things like cable internet and ADSL) is essentially impossible. almost all servers are running blacklists which have all of these addresses in a very large block of blacklists which will prevent them from accepting mail. the good side of this is that if you are infected with an email sending worm, it's less likely to propagate massively, the bad side is that no home email servers. the best thing you can do, is to setup your server to send to another smtp server as a client versus as a server, using typical client authentication. Receiving email is another story. you can try setting your port to something other than 25 if your ISP is blocking 25, but then you might need to futz with DNS entries to make sure other ISPs know where to send the email to.