WP Mail SMTP: when using SMTP mailer – disable SSL verification

add_filter('wp_mail_smtp_custom_options', function( $phpmailer ) {

	$phpmailer->SMTPOptions = array(

		'ssl' => array(

			'verify_peer'       => false,

			'verify_peer_name'  => false,

			'allow_self_signed' => true

		)

	);

	return $phpmailer;

} );