You can use the option -o in sendEmail to send a html email.
-o message-content-type=html to specify the content type of the email.
-o message-file to add the html file to the email content.
I have tried this option in a shell scripts, and it works.
Here is the full command:
/usr/local/bin/sendEmail -f [email protected] -t "[email protected]" -s \
smtp.test.com -u "Title" -xu [email protected] -xp password \
-o message-charset=UTF-8 \
-o message-content-type=html \
-o message-file=test.html