There seems to be an error in your script for cases where a bounce message (in my case provided via Amazon SNS) contains an apostrophe. Here a relevant message from my error log:
[04-Aug-2016 04:11:15 UTC] WordPress database error You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 's email address for typos or
550-5.1.1 unnecessary spaces. Learn more at
550 5.1' at line 1 for query INSERT INTO `wpmlbounces` (`id`, `email`, `count`, `status`, `history_id`, `created`, `modified`) VALUES ('', 'xyz@gmail.com', '1', '5.1.1 - smtp; 550-5.1.1 The email account that you tried to reach does not exist. Please try
550-5.1.1 double-checking the recipient's email address for typos or
550-5.1.1 unnecessary spaces. Learn more at
550 5.1.1 https://support.google.com/mail/answer/6596 k9si7074437qte.22 - gsmtp', '', '2016-08-04 04:11:15', '2016-08-04 04:11:15') made by require('wp-blog-header.php'), require_once('wp-load.php'), require_once('wp-config.php'), require_once('wp-settings.php'), do_action('init'), call_user_func_array, wpMail->init, wpMailPlugin->bounce, wpmlBounce->save