Configure SENDMAIL in Linux 6 to send alerts using GMAIL

To send Email from Linux (Centos) shell using simple mail commands, you need to setup sendmail and use G-MAIL as relay (comes in handy). This was also required in radius manager setup where radius system sends various alerts to user like expiry alerts, quota alerts and my own customized alerting events.

First install required items.

yum -y install sendmail mailutils mailx sendmail-bin sendmail-cf cyrus-sasl-plain

Now issue following command to create Gmail authentication file in a folder in which you will add Gmail user name and password.

# mkdir -m 700 /etc/mail/authinfo
# cd /etc/mail/authinfo/

Next we need to create an authentication file with following contents. You can name it as you like. In this example I have configured it gmail-pass:

Create File and add following:-

# vi gmail-pass
      AuthInfo: "U:root" "I:email@gmail.com" "P:email_password"

[Note: Replace the above with your gmail id and password]

In the next step we will need to create a hash map for the above authentication file:

# makemap hash gmail-pass < gmail-pass

Configure your sendmail

Now add bellow lines into your /etc/mail/sendmail.mc configuration file. Make sure you add them at end, but right above first “MAILER” definition line:

Example your file may look like this before editing (last few lines)

dnl MASQUERADE_DOMAIN(localhost)dnl
dnl MASQUERADE_DOMAIN(localhost.localdomain)dnl
dnl MASQUERADE_DOMAIN(mydomainalias.com)dnl
dnl MASQUERADE_DOMAIN(mydomain.lan)dnl
MAILER(smtp)dnl
MAILER(procmail)dnl
dnl MAILER(cyrusv2)dnl

You need to add the following lines above MAILER(smtp)dnl line

# vi /etc/mail/sendmail.mc

now paste following and save changes

# Adding config for gmail #

define(`SMART_HOST',`[smtp.gmail.com]')dnl
define(`RELAY_MAILER_ARGS', `TCP $h 587')dnl
define(`ESMTP_MAILER_ARGS', `TCP $h 587')dnl
define(`confAUTH_OPTIONS', `A p')dnl
TRUST_AUTH_MECH(`EXTERNAL DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl
define(`confAUTH_MECHANISMS', `EXTERNAL GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl
FEATURE(`authinfo',`hash -o /etc/mail/authinfo/gmail-pass.db')dnl

# End config for gmail #

Now your sendmail.mc file will look like as following after editing (last few lines)

dnl MASQUERADE_DOMAIN(localhost.localdomain)dnl
dnl MASQUERADE_DOMAIN(localhost)dnl
dnl MASQUERADE_DOMAIN(mydomainalias.com)dnl
dnl MASQUERADE_DOMAIN(mydomain.lan)dnl

# Adding config for gmail #

define(`SMART_HOST',`[smtp.gmail.com]')dnl
define(`RELAY_MAILER_ARGS', `TCP $h 587')dnl
define(`ESMTP_MAILER_ARGS', `TCP $h 587')dnl
define(`confAUTH_OPTIONS', `A p')dnl
TRUST_AUTH_MECH(`EXTERNAL DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl
define(`confAUTH_MECHANISMS', `EXTERNAL GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl
FEATURE(`authinfo',`hash -o /etc/mail/authinfo/gmail-pass.db')dnl

# End config for gmail #

MAILER(smtp)dnl
MAILER(procmail)dnl
dnl MAILER(cyrusv2)dnl

Now we need to re-build sendmail’s configuration. Run following command to do so.

# make -C /etc/mail

Reload sendmail service:

# /etc/init.d/sendmail reload

In case, sendmail doesn’t restart successfully, ensure Postfix is not running. Stop it if required.

service postfix status
service postfix stop

Also, ensure/enable sendmail autostartup:-

# chkconfig --list sendmail
# chkconfig --add sendmail

TEST VIA SENDING MAIL FROM SHELL

Now you can send email from your command line using mail command:

$ echo  "SendMail configuration - Test Mail" | mail -s "Testing Sendmail" email@ymail.com

TO check its status via Logs, you can view file

# tail -f /var/log/maillog