ClamAV

ClamAV is a useful antivirus toolkit designed to detect threats in email messages and other files. It provides you with multiple detection mechanisms for malware, trojans and other security threats.
The Internet is an endless source of information but is also includes multiple security threats which can be copied on your computer without your knowledge. This is why you should always have an antivirus installed on your computer and keep it updated on a regular basis.
ClamAV is one of the software solutions for keeping your data safe and prevent viruses from accessing your files. It is optimized for email servers which makes it more suitable for network administrators than for casual users.
The package includes multiple command line tools which are designed to perform multi-threaded virus scans, on-demand scans and virus database updates. It does not include a graphical user interface so you need to set up the engine by editing the sample configuration files.
Since it performs all operations with command line arguments, the app has a small footprint and requires minimum resources to detect the unwanted viruses which is important when you need it for processing a large number of email messages and attachments.
Although the installer does not include tutorials or help files, the can access the online resources from the developer website. As it is a open-source application you can also contribute to its development or share opinions with a large user community.
If you need a lightweight virus scanner for your email gateway, ClamAV is one of the available solutions. However, you need to test its detection rate for yourself in order to select the best tool for your needs.