Mail server

Mail server

Mail server is used to send the email to local or remote systems.

Structure of mail server

Mail Transfer Agent

The Mail Transfer Agent (MTA) is the part of the email system that does much of the work of transferring the email messages from one computer to local or remote systems with /usr/bin/sendmail program. Once configured correctly, most users will not have any direct interaction with their chosen MTA unless they wish to re-configure it for any reason.

Mail User Agent

This is the part of the system that the typical user is likely to be most familiar with. The Mail User Agent (MUA), or mail client, is the application that is used to write, send and read email messages. Anyone who has written and sent a message on any computer has used a Mail User Agent of one type or another.

Mail Delivery Agent

 The MDS delivers mail to the recipients .

The Mail Delivery Agent (MDA) sits in the background and performs filtering on the email messages between the Mail Transfer Agent and the mail client (MUA). The most popular form of MDA is a spam filter to remove all the unwanted email messages from the system before they reach the inbox of the user’s mail client (MUA).

SMTP

SMTP is an acronym for Simple Mail Transport Protocol. This is the protocol used by the email systems to transfer mail messages from one server to another. This protocol is essentially the communications language that the MTAs use to talk to each other and transfer messages back and forth.

Relaying: Forwarding a submitted mail to another mail server for delivery when the distance is long.

If the machine needs to pass mail to another mail server to get out to the Internet, the hostname of the mail server should be defined as the Relay Host.

Postfix mail server Configuration

Service profile

Service: postfix

Package: postfix

Port no:25(TCP)

Configuration file: /etc/postfix/main.cf

Script file: /etc/ init.d/postfix

Daemons: postfix

Objective :To act as mail transfer agent

Install the postfix package

[root@mailserver~]#yum install  postfix* -y

Edit main Configuration file

[root@mailserver~]#vi /etc/postfix/main.cf

 myhostname=mailserver.raju.com

 mydomain=raju.com

myorigin=desktop1

mynetworks=192.168.0.0/24

#SMTP authentication for our users with postfix

smtpd_sasl_auth_enable = yes 

smtpd_sasl_local_domain = raju.com

smtpd_recipient_restrictions = permit_mynetworks,permit_sasl_authenticated,reject_unauth_destination 

smtpd_sasl_security_options = noanonymous

:wq!

[root@mailserver~]chkconfig postfix on

[root@mailserver~]#service postfix restart

Dovecot

Dovecot is one of the popular POP3/IMAP server which needs MTA like Postfix to work properly.

[root@mailserver~]#yum install  devcot* -y

[root@mailserver~]#vi /etc/devcot

 Protocols=imap pop3

disable_plaintext_auth=no

#SMTP authentication for users with dovecot.

#Look for the line that starts with auth default, before that insert the lines below.

auth default {

mechanisms = plain login

passdb pam {

}

userdb passwd {

}

socket listen {

client {

path = /var/spool/postfix/private/auth

mode = 0660

user = postfix

group = postfix

}

}

}

#rename previous auth default to auth default2. If you dont rename this then dovecot server will give you error like multiple instances of auth default

:wq!

[root@mailserver~]chkconfig postfix on

[root@mailserver~]#service mailserver restart

[root@mailserver~]#chkconfig devcot on

[root@mailserver~]#service devcot restart

 Create user for testing

[root@mailserver~]#useradd koti

 [root@mailserver~]#useradd raju

logon to raju

[root@raju]mail  –s  hello  koti@mailserver.raju.com