this was the problem:
the admin_email function sent the email like an anonymous user without headers, the send_ppemail function (used for notifications email) send the emails with the Administrator Email Address and complete headers.
i have edited pp-inc and in the admin email function i have added this code (copied from send_ppemail function) after this line : $email_from = "From: {$Globals['adminemail']}";
Code:
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then i changed this line: mail( $useremail, $subject, $letter, $email_from );
with this line: mail( $useremail, $subject, $letter, $headers );
Now is was working fine, the emails are sent "from the administrator account" and gmail accept the deletion and approve emails