v  A mail server (also known as a mail transfer agent or MTA, a mail transport agent, a mail router or an Internet mailer) is an application that receives incoming e-mail from local users (people within the same domain) and remote senders and forwards outgoing e-mail for delivery. A computer dedicated to running such applications is also called a mail server.

v  Microsoft Exchange, qmail, Eximand sendmailare among the more common mail server programs.

v  The mail server works in conjunction with other programs to make up what is sometimes referred to as a messaging system. A messaging system includes all the applications necessary to keep e-mail moving as it should. When you send an e-mail message, your e-mail program, such as Outlook or Eudora, forwards the message to your mail server, which in turn forwards it either to another mail server or to a holding area on the same server called a message store to be forwarded later. As a rule, the system uses SMTP(Simple Mail Transfer Protocol) or ESMTP(extended SMTP) for sending e-mail, and either POP3(Post Office Protocol 3) or IMAP(Internet Message Access Protocol) for receiving e-mail.

v  Mail servers support a large number of the protocols such as SMTP, ESMTP, POP3 and IMAP.

v  SMTP (Simple Mail Transfer Protocol) is a TCP/IPprotocolused in sending and receiving e-mail.

v  SMTP usually is implemented to operate over Internet port25.

v  ESMTP (Extended Simple Mail Transfer Protocol) specifies extensions to the original protocolfor sending e-mail that supports graphics, audio and video files, and text in various national languages. The original Internet protocols for sending e-mail are described in Request for Comments (RFC) 822, Standard for the Format of ARPA Internet Text Messages, and in RFC 821, Simple Mail Transfer Protocol (SMTP).

v  Currently, most commercial e-mail servers and clients support ESMTP.

v  POP3 (Post Office Protocol 3) is the most recent version of a standard protocol for receiving e-mail. POP3 is a client/serverprotocolin which e-mail is received and held for you by your Internet server.

v  The conventional port numberfor POP3 is 110.

v  IMAP (Internet Message Access Protocol) is a standard protocolfor accessing e-mailfrom your local server.

v  POP3 and IMAP deal with the receiving of e-mail from your local server and are not to be confused with Simple Mail Transfer Protocol (SMTP), a protocol used for exchanging e-mail between points on the Internet. Typically, SMTP is used for sending only and POP3 or IMAP are used to read e-mail.