The error is telling you that the host techmahindra.com can't be found in DNS.
Your code is okay, it's a DNS issue either on their side or yours (if that is a valid host).

Send a test email from hwnej05 to the email address:
$ mailx -s"test" youraddress@techmahindra.com < /dev/null

If you get the same type of error, then you know that your code was okay (as long as the spelling of the techmahindra.com is correct).

Then try to look up the mx address of techmahindra.com
$ nslookup
> set type=mx
> techmahindra.com

You should get info such as
If you don't get a response on the lookup, then your DNS isn't finding the MX record of the domain you are trying to send to and the email won't be sent.