PHP email issue only working within my domain - php

Question

I have a PHP code hosted on godaddy linux shared hosting
My script is sending email to my domain but not external domain.
I can send an email from hotmail to my domain but cannot send email from my domain to hotmail.
My domain is not listed as spam
Here is the PHP code I am using and working when sending to my domain.
headers = "From: webmaster#mydomain.com \n";
$headers .= 'X-Mailer: PHP/' . phpversion();
$headers .= "MIME-Version: 1.0\r\n";
$headers .= "Content-Type: text/html; charset=iso-8859-1\n";
mail($email, $subject, $txt, $headers)
So why is it not getting delivered outside my domain?
I am able to send an email using the script but only on my own adress. me#myserver.com. When I receive it the from adress is wrong. Its not the one i have included in the headers

Answer 1

I'm guessing that your not authenticated your emails before sending (using SMTP). This is commonly blocked by mail servers as it cannot verify where the actual email is coming from. Try authenticating your emails using your SMTP credentials through your Godaddy server and see if that fixes it.

Answer 2

From their documentation,
Two non-CGI form mailers are included in Linux shared hosting account
default files: webformmailer.php and gdform.php. They reside in the
root directory of your hosting account. Incorporating either of these
scripts into your website creates a form to capture user information
and email it to a specified address
SPECIFYING AN EMAIL ADDRESS FOR THE PHP FORM MAILER
To use their PHP form-mailer, you must specify an email address where you want the contents of your form sent to.
Form-mailers cannot send from #aol.com, #gmail.com, #hotmail.com,
#msn.com, or #yahoo.com addresses.
To Specify the Email Address for the Form-Mailer
Log in to your GoDaddy account.
Click Web Hosting.
Next to the hosting account you want to use, click Manage.
In the Tools section of the Hosting Control Panel, click the Form
Mail icon.
Under the Forms Email Address section, type the email address you
want to use with your form-mailer.
Click Continue.
Verify that this is the address you want to use with your
form-mailer, and click Update.
For more information, Please read this page
UPDATE::
The best thing to do is check what PEAR extensions GoDaddy have on there hosting, if they have PEAR mail, you can use that. If not, then you should try using authenticated mail sending.
<?php
include('Mail.php');
$recipients = 'joe#example.com';
$headers['From'] = 'richard#example.com';
$headers['To'] = 'joe#example.com';
$headers['Subject'] = 'Test message';
$body = 'Test message';
$params['sendmail_path'] = '/usr/lib/sendmail';
// Create the mail object using the Mail::factory method
$mail_object =& Mail::factory('sendmail', $params);
$mail_object->send($recipients, $headers, $body);
?>
Mail::send() – sends a mail