Postfix Modification


I have changed the port to 1234 for the auth /TLS connection however you can still login and send mail from port 25 I would like port 25 not to accept connections from my users and force them to use of the secure connection and only allow port 25 to send and receive mail from other servers. I have made modifications but so far every thing I have tried also effects incoming mail. Can any one offer advice on how this can be achieved?