Drupal 8 Custom Module Stop Sending Emails Filter by Email Addresses

I am building a custom module using hook_mail_alter in Drupal 8 which stops the system from sending emails to a selected email address. My current module stops sending any emails for some reasons. I need help to figure out why.

<?php
use Drupal\Core\Mail\MailManagerInterface;

/**
* Implements hook_mail_alter
*/

function terminate_emails_mail_alter(&$message) {

    //filter by email address, which is not working
    if($message['to'] = 'example@gmail.com') {

    //stop sending emails
      $message['send'] = FALSE;    
    }
}