You could add a note on that bug report, or make a new one. I am no expert in this but bluehost may be the issue perhaps? some blockage some place… As in the bug report, it’s not a problem which has been verified by many people.
sendMail($email, “Goodbye from our newsletter”,“You have been unsubscribed from our newsletters and will not receive any more emails. If this is in error, please contact us.” , system_messageheaders($email), ‘’, true);