Line of code to update in joomla administrator/components/com_messages/models/message.php


//line 300
$siteURL = JUri::root() . 'administrator/index.php?option=com_messages&view=message&message_id=' . $table->message_id;
$subject = sprintf($lang->_('COM_MESSAGES_NEW_MESSAGE_ARRIVED'), $sitename);
$msg = $table->message;

// Send the email
JFactory::getMailer()->sendMail($fromUser->email, $fromUser->name, $toUser->email, $subject, $msg,true);