Firewall
Firewalls prevent unauthorized access to a computer or network. Firewalls can be built of hardware, software, or a combination of both, and erect barriers between the desired computer or network and users attemptong to gain access without suitable credentials or privileges. Email Firewalls block email from being delivered, while system-wide Firewalls prevent unauthorized access of any kind, including logging into the network, email reception or – in some cases- even simple browsing.

