Why Email Server in Linux are popular?

Supports POP3, IMAP and Web mail access. These are standard services that ideally should be available in any mail system for flexible email access.

Is extremely fast, reliable and scalable. Linux performs well and its uptime is very, very good.

Does not require expensive hardware. Thanks to its fast and efficient services, expensive high end hardware is not necessary.

Is very secured. The Linux operating system is very difficult to exploit. The National Security Agency even contributed to allow Linux to support even stronger levels of security.

Has a powerful anti-spam filter. SpamAssassin uses a wide variety of local and network tests to identify spam signatures.

Has an effective and regularly updated anti-virus. The open source nature of Clam Antivirus allows it to respond to new viruses even faster than commercial antivirus softwares.

Has small to zero (as in free) software cost depending on your support needs. Depending on your support needs, you have the option of using a community supported Linux or a company supported one.

Works with Microsoft Active Directory. You can integrate Microsoft Active Directory user accounts and distribution list into your Linux mail server to simplify administration.