Praetor is dependent upon the Microsoft IIS Virtual SMTP Server which unfortunately uses a single global setting for what port to transmit messages.
Thus if it is set to any non-standard port when Praetor coexists on the same machine as your mail server that will receive filtered messages on port 28, then any Internet-bound messages will also be sent using this same port. Since Internet mail servers are expecting to get mail transmissions on port 28, no outbound messages can be transmitted by the IIS SMTP Server.