HowTo - Linux Mail Server - Postfix
If you want to send or receive an email you should have a mail server capable of sending and receiving mail across the Internet, in this post we will discuss Linux mail server and how SMTP protocol (the standard protocol for mail transport across the internet) works as well as other mail-related protocols, like Post Office Protocol (POP) and Internet Message Access Protocol (IMAP) and the relationship between them. Linux SMTP Mail Server SMTP (Simple Mail Transfer Protocol) defines how a mail is sent from one host to another, it does not define how the mail should be stored or how it is displayed, and it is also system independent, which means the sender and receiver could have different operating systems. SMTP requires only that a server is able to send straight ASCII text to another server, and this is done by connecting to the server on port 25 which is the standard SMTP port. Most Linux distros today are shipped with two of the most common implementation of SMTP which are sendmail and postfix. Sendmail is a popular open source mail server implementation used by many Linux distros, but it has a little complex design and less secured.