Exim is an open source email server, it's a comfortable and running with Unix or Linux Operating system. The Exim security record is much better than sendmail. Advanced features are queue handling, address routing and testing. It's an integrated with contnet scnanning, spam and virus scanners.

How to install Exim :

Download the comfortable repo file and install it
# wget http://epel.mirror.net.in/epel/6/x86_64/epel-release-6-8.noarch.rpm

# rpm -ivh epel-release-6-8.noarch.rpm

Intall exim-mysql package by yum command,
# yum install -y exim-mysql

Stop the postfix and enable exim server as set default MTA
# service postfix stop
# chkconfig postfix off

Set Exim as the default MTA
# alternatives --config mta

There are 2 programs which provide 'mta'.

  Selection    Command
*+ 1           /usr/sbin/sendmail.postfix
   2           /usr/sbin/sendmail.exim

Enter to keep the current selection[+], or type selection number: 2

Set auto start on boot time
# chkconfig exim on

# service exim start

Start the exim service,
# /etc/init.d/exim start

Starting exim:                                             [  OK  ]
0 processes (antirelayd) sent signal 9

Exim Installed Path:
# whereis exim

exim: /usr/sbin/exim /etc/exim /usr/lib/exim /usr/share/man/man8/exim.8.gz

To find out the version:
# exim -bV | head -1

Exim version 4.72 #1 built 28-Oct-2012 18:32:42

Basic File Location:
Configuration File : /etc/exim/exim.conf
Main Log File  : /var/log/exim/main.log
Panic Log File : /var/log/exim/panic.log

Do you require to determine whether email sending from the  server
# mail -s "Test Email" hostfortest@gmail.com < /dev/null

Null message body; hope that's ok

Email sent logs:

2014-01-18 10:09:07 1WxGXz-a010DH-L0 <= root@host.hostname.com U=root P=local S=573
2014-01-18 10:09:10 1WxGXz-a010DH-L0 => hostfortest@gmail.com R=dnslookup T=remote_smtp H=gmail-smtp-in.l.google.com [] X=UNKNOWN:ECDHE-RSA-AES128-GCM-SHA256:128
2014-01-18 10:09:10 1WxGXz-a010DH-L0 Completed

If you could not find the mail package in system install in a single command,
yum install mailx