Postfix question

Dear all! Is it possible to set up postfix in the following way, so that it would permit sending mail with unathorized access from internal private network, and at the same time serve as secured password-authorized SMTP to external public network in other words: if i would like to send mail from internal netwrok, i just specify my server as usual SMPT without auth, and if i want to use it from outside, i configure my mail client to use it with SSL enabled and with user/password auth. Any ideas will be highly welcomed!