Linux mail command using sendmail

mail.sh:
-------------------------------------------------------------
while read line
do
        if [ -n "`echo $line | grep \"#SUBJECT#\"`" ]
        then
                echo "Subject: message here" >> mail.txt
        elif [ -n "`echo $line | grep \"#CONTENT#\"`" ]
        then
                echo "content message here" >> mail.txt
        else
                echo $line >> mail.txt
        fi
done < mail_sample
sendmail -t -oi -f "sender@sender.com" < mail.txt
-------------------------------------------------------------

mail_sample:
----------------------------------------

From: sender@sender.com

To: receiver@receiver.com

Cc:  receiver@receiver.com

Content-type: text/html; charset=UTF-8

#SUBJECT#

#CONTENT#

----------------------------------------