The mail command can be used to send an email to a user's inbox. Before the mail command can be used, the mailx package will need to be installed.

[root@server1 ~]# apt-get install mailutils
[root@server1 ~]# yum install mailx

If using sendmail, this command will send an email.

[root@server1 ~]# mail -s "Hello World" user1@example.com

For example, this script sends an email to root. 

#!/bin/bash
sender="From: Firstname Lastname"
recipient="root@server1"
subject="Hello World"
message="How are you today?"

mailx -a "$sender" -s "$subject" $recipient <<< $message

An if statement can be used to send conditional emails to the superuser. In this example, if foo equals 1, an email is sent to root@example.com. foo is set to 1, so when this script is executed, an email will be sent to root@example.com.

1  #!/bin/bash
2  foo=1
3  if [ $foo -eq 1 ]
4  then
5    echo "Hello World" | mailx -s "Test Email" root@example.com
6  fi

More TBD . . .