Email Security Appliances
Although a firewall will prevent a degree of email based threats, dedicated email security appliances, either physical or virtual, are designed purely to focus on this area of vulnerability. Providing superior protection from inbound and outbound threats - including spam, phishing, zombie attacks, malware, and even ransomware, they also minimize deployment, administration and bandwidth expenses.
A firewall is a security device which can be either hardware and/or software based. The purpose of a firewall is to permit or deny proxy data coming in and out of your computer system and/or network. A firewall may simply be hardware deep packet inspection, or linked to various software signatures looking at anti-virus, anti-spam, or phishing threats. In this latter case they are often referred to as UTM devices (Unified Threat Management). If a higher degree of security is required, then a Next Generation Firewall (NGFW) should be considered.