A program or set of programs designed to keep unauthorized users or messages from accessing a private network. The firewall usually has rules or protocols that authorize or prohibit outside users or messages. In email, a firewall can be designed so thast messages from domains or users listed as suspect because of spamming, hacking or forging will not be delivered.

Building Your Business with an Opt-in List
Before revealing the secrets of the trades, here are myths and fallacies that need to be cleared before one indulges into building an opt-in list.