This article briefly sorted out the steps of how to install and configure SendMail to send mail on Linux server. This article is not configuring mail server. The specific test environment is CentOS Linux release 7.2.1511 (Core). If there are differences between special platforms, please take the actual situation as the criterion.

Linux System Version View

Check and understand the system version information, mainly if you use rpm installation, you need to download the appropriate version.

[root@mylnx06 ~]# more /etc/redhat-release 

CentOS Linux release 7.2.1511 (Core)

Check whether the sendmail component is installed

As shown below, there is no sendmail component installed on the server. Then we can install sendmail components directly using yum.

[root@mylnx06 ~]# rpm -qa | grep sendmail

[root@mylnx06 ~]# yum list sendmail

Loaded plugins: fastestmirror, langpacks

Loading mirror speeds from cached hostfile

 * epel: ftp.cuhk.edu.hk

Available Packages

sendmail.x86_64                                       8.14.7-4.el7                    base

Use yum to install sendmail components. Of course, you can install them in other ways. There is no introduction here.

[root@mylnx06 ~]# yum install sendmail.x86_64 

Loaded plugins: fastestmirror, langpacks

Loading mirror speeds from cached hostfile

 * epel: ftp.cuhk.edu.hk

Resolving Dependencies

--> Running transaction check

---> Package sendmail.x86_64 0:8.14.7-4.el7 will be installed

--> Finished Dependency Resolution

Dependencies Resolved

========================================================================================================================

 Package                     Arch                      Version                            Repository               Size

========================================================================================================================

Installing:

 sendmail                    x86_64                    8.14.7-4.el7                       base                    722 k

Transaction Summary

========================================================================================================================

Install  1 Package

Total download size: 722 k

Installed size: 1.6 M

Is this ok [y/d/N]: y

Downloading packages:

sendmail-8.14.7-4.el7.x86_64.rpm                                                                 | 722 kB  00:00:00     

Running transaction check

Running transaction test

Transaction test succeeded

Running transaction

  Installing : sendmail-8.14.7-4.el7.x86_64                                                                         1/1 

  Verifying  : sendmail-8.14.7-4.el7.x86_64                                                                         1/1 

Installed:

  sendmail.x86_64 0:8.14.7-4.el7                                                                                        

Complete!

[root@mylnx06 ~]# 

Edit / etc/aliases file

Sendmail has a very practical function, which is to alias each account and use a file in / etc/aliases to do user name conversion. So this configuration file is available or not, depending on your needs.

[root@mylnx06 ~]# vi /etc/aliases

#

#  Aliases in this file will NOT be expanded in the header from

#  Mail, but WILL be visible over networks or from /bin/mail.

#

#       >>>>>>>>>>      The program "newaliases" must be run after

#       >> NOTE >>      this file is updated for any changes to

#       >>>>>>>>>>      show through to sendmail.

#

# Basic system aliases -- these MUST be present.

mailer-daemon:  postmaster

postmaster:     root

# General redirections for pseudo accounts.

bin:            root

daemon:         root

adm:            root

lp:             root

sync:           root

shutdown:       root

halt:           root

mail:           root

news:           root

uucp:           root

operator:       root

games:          root

gopher:         root

ftp:            root

nobody:         root

radiusd:        root

nut:            root

dbus:           root

vcsa:           root

canna:          root

wnn:            root

rpm:            root

nscd:           root

pcap:           root

apache:         root

webalizer:      root

dovecot:        root

fax:            root

quagga:         root

radvd:          root

pvm:            root

amandabackup:           root

privoxy:        root

ident:          root

named:          root

xfs:            root

gdm:            root

mailnull:       root

postgres:       root

sshd:           root

smmsp:          root

postfix:        root

netdump:        root

ldap:           root

squid:          root

ntp:            root

mysql:          root

desktop:        root

rpcuser:        root

rpc:            root

nfsnobody:      root

ingres:         root

system:         root

toor:           root

manager:        root

dumper:         root

abuse:          root

newsadm:        news

newsadmin:      news

usenet:         news

ftpadm:         ftp

ftpadmin:       ftp

ftp-adm:        ftp

ftp-admin:      ftp

www:            webmaster

webmaster:      root

noc:            root

security:       root

hostmaster:     root

info:           postmaster

marketing:      postmaster

sales:          postmaster

support:        postmaster

# trap decode to catch security attacks

decode:         root

# Person who should get root's mail

#root:          marc

As shown in the screenshot below, if I configure an alias root, configure to receive mail (the following mail is just a template)

Modify the configuration file sendmail.cf

Modify / etc/mail/sendmail.cf to add the corresponding DS, followed by the IP address of the mail server. Configuration according to the actual situation. In fact, this configuration file, if necessary, there are a lot of need to configure, refinement, here only describes the simplest configuration.

# host/domain names ending with a token in class P are canonical

CP.

# "Smart" relay host (may be null)

DS[xxx.xxx.xxx.xxx]

# operators that cannot be in local usernames (i.e., network indicators)

CO @ % !

# a class with just dot (for identifying canonical names)

Restart sendmail service

[root@mylnx06 ~]# service sendmail status

Redirecting to /bin/systemctl status  sendmail.service

● sendmail.service - Sendmail Mail Transport Agent

   Loaded: loaded (/usr/lib/systemd/system/sendmail.service; enabled; vendor preset: disabled)

   Active: inactive (dead)

Feb 22 10:29:45 azlnx06 systemd[1]: Stopped Sendmail Mail Transport Agent.

[root@mylnx06 ~]# service sendmail start

Redirecting to /bin/systemctl start  sendmail.service

[root@mylnx06 ~]# service sendmail status

Redirecting to /bin/systemctl status  sendmail.service

● sendmail.service - Sendmail Mail Transport Agent

   Loaded: loaded (/usr/lib/systemd/system/sendmail.service; enabled; vendor preset: disabled)

   Active: active (running) since Wed 2017-02-22 10:42:02 HKT; 5s ago

  Process: 46129 ExecStart=/usr/sbin/sendmail -bd $SENDMAIL_OPTS $SENDMAIL_OPTARG (code=exited, status=0/SUCCESS)

  Process: 46116 ExecStartPre=/etc/mail/make aliases (code=exited, status=0/SUCCESS)

  Process: 46115 ExecStartPre=/etc/mail/make (code=exited, status=0/SUCCESS)

 Main PID: 46131 (sendmail)

   CGroup: /system.slice/sendmail.service

           └─46131 sendmail: accepting connections

Feb 22 10:42:02 azlnx06 systemd[1]: Starting Sendmail Mail Transport Agent...

Feb 22 10:42:02 azlnx06 sendmail[46124]: alias database /etc/aliases rebuilt by root

Feb 22 10:42:02 azlnx06 sendmail[46124]: /etc/aliases: 77 aliases, longest 17 bytes, 792 bytes total

Feb 22 10:42:02 azlnx06 sendmail[46131]: starting daemon (8.14.7): SMTP+queueing@01:00:00

Feb 22 10:42:02 azlnx06 systemd[1]: PID file /run/sendmail.pid not readable (yet?) after start.

Feb 22 10:42:02 azlnx06 systemd[1]: Started Sendmail Mail Transport Agent

Test Mail Service

As shown below, use the mail command to test whether mail is received successfully. If it succeeds, it means that OK was configured before. If no mail was received, the log must be checked and the problem diagnosed according to the specific error information.

[root@mylnx06 ~]# cat > test.txt

it is only test

^Z

[1]+  Stopped                 cat > test.txt

[root@mylnx06 ~]# mail -s "test" konglb@xxxx.com < test.txt 

[root@mylnx06 ~]# 

[azrlnx06azlnx06 ~]$ echo 'it is only a test' | mail -s "test eamil"  konglb@xxxx.com

[azrlnx06@azlnx06 ~]$