How to send message in html format using shell script

I want to send email message in html format using unix shell script. I use sendEmail command in my script to send email message. The syntaxt of the sendEmail command is as follows:
$sendEmail -f <email> -t <email> -u $subject -s smtpserver:port -o message-file=html

I should be able to rediret the output of script in HTML formatted file
OR How do I create HTML file using Shell Script.

Thanks and Regards

You may want to copy a given html file into the message body:

sendEmail [blabla] -m "$( cat html.file )" [blabla]