Unable to send the email in formatted way

Then this should also work:

#!/usr/bin/bash
/usr/sbin/sendmail -oi -t <<EOF
From: abc@xyz.com
To: def@xyz.com
Subject: GAP Report
Content-Type: text/html; charset=us-ascii
Content-Transfer-Encoding: 7bit
MIME-Version: 1.0
<pre>
$(cat "$FILE.txt")
</pre>
EOF

@Scrutinizer
Yes that also working perfectly.
Thanks once again.

So problem was determining "white spaces" ?

<br>