mad-watches

I am new to php. I have instralled oscommerce and got it working. The probelm that I am having is when a new customer registers it errors sending them an email. It also errors when they purches stuff. I can send the customer an email from the admin section. So my email setting are working. Here is the erroe that I am getting. PHP Warning: mail() [<a href='function.mail'>function.mail</a>]: SMTP server response: 501 5.5.4 Invalid Address in C:\Inetpub\watches\catalog\includes\classes\email.php on line 520 PHP Warning: mail() [<a href='function.mail'>function.mail</a>]: SMTP server response: 501 5.5.4 Invalid Address in C:\Inetpub\watches\catalog\includes\classes\email.php on line 520 Here is the line in the php script that is refeanced. return mail($to_addr, $subject, $this->output, 'From: ' . $from . $this->lf . 'To: ' . $to . $this->lf . implode($this->lf, $this->headers) . $this->lf . implode($this->lf, $xtra_headers)); } else { return mail($to, $subject, $this->output, 'From: '.$from.$this->lf.implode($this->lf, $this->headers).$this->lf.implode($this->lf, $xtra_headers)); } Can any one help?