A mail server (also known as a mail transfer agent or MTA, mail transport agent, mail router, or Internet mail) is an application that receives incoming email from local users (people within the same domain ) and remote senders and send the outgoing email for delivery. A computer dedicated to running such applications is also called a mail server. Microsoft Exchange, qmail, Exim and sendmail are among the most common mail server programs.
The mail server works together with other programs to do what is sometimes called a messaging system. A messaging system includes all the necessary applications to keep the email in motion 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 to another mail server or to a waiting area on the same server called a store of messages to be resubmitted later. As a general rule, the system uses SMTP (Simple Mail Transfer Protocol) or ESMTP (Extended SMTP) to send e-mail and POP3 (Mail Office Protocol 3) or IMAP (Internet Message Access Protocol) to receive e-mail .
