Not really no. Because all the mail servers on the internet are listening on port 25 (smtp) for incoming mail.
The use of other ports, like 465, 587 etc are generally for user access depending on the services provided to their own clients.
Your best bet is to do a few google searches and see if you can find other people trying to run mail servers behind Comcast and see what they did. The easiest way is the smarthost way - if you can find a comcast server to relay through.