the solution of their problem lies in the middle.
Return Path can't be set in headers, it must be set as additional mail() parameter. Like so:
PHP Code:
mail($to, $subject, $body, $headers, "-f".$return_path);
It should be also noted that it can't be set if PHP is running under Windows or is less than version 4.0.6.
These headers are correct:
PHP Code:
$headers .= 'From: Mr. Person<person@domain.com>'.$eol;
$headers .= 'Reply-To: Mr. Person<person@domain.com>'.$eol;
A combination of the above should get them through without any server config modifications.