A mail server (or email server) is a computer system that sends and receives email. In many cases, web servers and mail servers are combined in a single machine. However, large ISPs and public email services (such as Gmail and Hotmail) may use dedicated hardware for sending and receiving email.
In order for a computer system to function as a mail server, it must include mail server software. This software allows the system administrator to create and manage email accounts for any domains hosted on the server. For example, if the server hosts the domain name "techterms.com," it can provide email accounts ending in "@techterms.com."
Mail servers send and receive email using standard email protocols. For example, the SMTP protocol sends messages and handles outgoing mail requests. The IMAP and POP3 protocols receive messages and are used to process incoming mail. When you log on to a mail server using a webmail interface or email client, these protocols handle all the connections behind the scenes.
Mail server software is available for multiple platforms. The most popular mail server for Windows is Microsoft Exchange Server, an enterprise product used by large businesses. However, many other options exist, including Ipswitch IMail Server, IceWarp Mail Server, MailEnable, and hMailServer. Popular Linux options include Exim for sending mail and Dovecot and Courier for receiving mail.