Enterprise Mac Security: Mac OS X Snow Leopard

10.4. Port Management

Since the introduction of malware and spyware, it is becoming more common to restrict incoming and outgoing access on commonly used (and abused) ports, such as port 25. For example, if you don't need mail services in your environment (perhaps because e-mail is hosted elsewhere), then it is likely that you will want to eliminate outgoing SMTP traffic from passing through your router. If you're not hosting mail internally, you will also want to make sure that all inbound mail-related traffic (SMTP, as well as POP and IMAP) is being denied as well.

As discussed in previous chapters, most savvy network administrators will also restrict incoming access to their networks to all but a select number of ports, and for good reason. ...