How to let Sender know that Recipient isn’t receiving messages?

In the PHPmotion web site script > My Profile > Email Notifications a user can select yes or no,
which can turn on or off the User from receiving email notifications that a private message has
been received into the User's internal messaging inbox.

I'm looking for a solution that let's the Sender(of an internal message) know that the User(recipient) isn't receiving notifications by email.

In the emailcompose.php file these lines(below), are where I believe a modification can be added? Can you let me know if this is possible here?
Or how this can be accomplished? Any help will be appreciated.

if (notification_preferences($to_id, 'privatemessage') == true) {

// send pm notification email to recipients registartion email addy
$email_template    = 'email_templates/newmessage.htm';
$subject = $config['email_new_email'];

// at this point we do not have any email to send to
$to = $members_email;
$from = $config['notifications_from_email'];

//send email template to TBS for rendering of variable inside
$template = $email_template;
$inner_template1 = "themes/$user_theme/templates/inner_email_compose.htm";

$TBS = new clsTinyButStrong;
$TBS->NoErr = true;

$TBS->LoadTemplate("$template");
$TBS->tbs_show(TBS_NOTHING);
$message = $TBS->Source;

//load postage.php
include ('includes/postage.php');

Code (markup):

 

Is there an else to that if? If not, you could probably hook one on, and just send a message (internal or via email) to the sender of the original message telling him/her that the user s/he's trying to communicate with has turned off the email notification, and won't see the message unless s/he logs in.

 

Thanks for your reply.
Can you help me get started with code where if
'privatemessage') == false)
then an email goes back to any sender of an internal message?

I've attached the file (changed to .txt from .php).

Thanks for any help