58613 cpanel nameserver/mail problem

I need a cpanel guru to help solve a mail problem on my server. I have a php script that sends email from to people that enter their email address. The problem is that most of the email get bounced to my admin email address with this error: "See attached file" I have put the -at- to replace the symbol The script will send email to my ISP email account, but it doesn't seem to be able to send email to any other email addresses. It's not just this one script, it's all the email that is generated from scripts on the server. Please PMB if you have any other questions.