Feedback form is not working,

I created a feedback form in PHP and its not working on one server, but I tried the same script on different hosting server its working fine. I am using yahoo email address.

when I talked to the hosting provider, he told me to do email authentication. I don't know how to do this...

Plz help

Thanks in advance!

Here's some light reading that might get you started:
http://en.wikipedia.org/wiki/E-mail_authentication