$subject = 'Subject';
$headers = 'From: For Sur <for_sur@gmail.com>\r\n';
$headers .='Reply-To: For Sur <for_sur@gmail.com>\r\n';
$headers .='Return-Path-To: For Sur <for_sur@gmail.com>\r\n';

mail('recipient@gmail.com', $subject, $post[3], $headers);


#################
#and mail source#
#################

...blablabla...

Subject: Subject
From: "For Sur <for_sur@gmail.com>\r\nReply-To": "For Sur <for_sur@gmail.com>\r\nReturn-Path-To: For Sur <for_sur@gmail.com>\r\n