Cynthia,
I am still having the issue but I never mentioned initially that while I get the error, the emails send to my website email as well as back to the person who filled out the form, but it also sends a second email similar to what you mentioned above to my website email as well. So the client gets one mail, and my website email receives 2 mails!
In regards to the error I was receiving, I have been on to my hosts and they have queried the Outgoing server php file, but I have tried making adjustments as recommended and I still get the error. So after spending hours playing around with it, making adjustments and testing etc, I have given up! As a result, I have altered it so my clients won't receive the auto response but it just says 'Thanks. I will reply....' on my website.
Always Remember...... Everyday Is A School Day!