This article will show how to install and configure the above criteria for setting up a mail server for a domain.

Postfix:

    Postfix is a mail transfer agent (MTA) that delivers electronic mail across globe. It is also called as an SMTP server. Postifx can be integrated with spamfilters, dovecot and  complex SMTP-level access-policies

    To install postfix in a rpm based machines run the below command,


    The default path of the config files are found under this directory /etc/postfix.

    The main.cf file is the core of your mail server configuration. The default main.cf file lists only a portion of the nearly 300 Postfix parameters. Most Postfix parameters do not need to be changed, but the flexibility is there when it’s required. The path for the main.cf file is /etc/postfix/main.cf

    The next important config file is the master.cf file. The master daemon uses the master.cf file for its configuration information. The master.cf file contains a line for each Postfix service or transport.
   
    Each line has columns that specify how each program should run as part of the overall Postfix system. Most of all the master.cf file can be edited for additional features such as SMTP authentication,etc.,. Since this is a simple mail server setup, we will not working on this file.

    Whenever you made changes to these files the postfix application should be reloaded or restarted.


or


Changes to be done on main.cf file:

    Since we are going to setup a global access mail server to receive mails from external world hence change the inet_interfaces to all from 127.0.0.1


Add the below lines on your main.cf files,


Your myhostname will be your mail server name.

Create the below files that you have mentioned on your main.cf files,


Creating .db files:

    You can create db files once adding a new file using postmap command, the same can be used to update the .db files too. Update their .db files on every changes, The reason for using .db files is postfix is able to lookup information in hashes faster than a normal text file.

valias.txt	Your user emails associated with the username.
relay_recipients	Defines the list of valid email addresses for the domain hosted.
relay_domains	Domains that has been relayed.
vhosts.txt	Domains hosted on this mail server.
vmaps.txt	Contains virtual email address and mailbox location.
sender_access	Allows particular senders to send mails to your mail server.
recipient_access	Used for access control.
client_access	Used for access control.
helo_access	Used for access control.