ClamAV 
ClamAV is a cross-platform, open-source software antivirus toolkit. It helps to find different types of malicious software that could host a virus. It is specially designed for email scanning on mail gateways. It is a software developed for Unix. It has a third party of the version that is available for macOS,  OSF, Solaris, HP-UX, AIX, Linux, and the BSD. It offers a variety of utilities, including a flexible and scalable multi-threaded daemon, a command-line scanner, and a developed tool for fully automated database updates. 
Why you must get it: 
ClamAV can be used for many purposes like automatic database update, command-line scanning, and multi-threaded haunt that can be expanded and run as an antivirus engine from shared libraries. It helps find files such as spam mails. ClamAV is mostly used by the administrator systems for filtering e-mails or messages. The virus database is updated regularly to ensure reliable protection for your system. This software also supports files like RAR, Zip, CHM, Tar, Ole2, Bzip2, Cabinet, SIS formats, BinHex and other mail formats like ELF executables, portables wxecutable files that have been compressed with UPX, FSG, NsPack, Petite, MEW, Upack etc. Other than this, it also supports word documents like HTML, RTF or Rich Text Format, PDF (Portable Document Format), and Microsoft.