phpmailer: unset SMTPAutoTLS

wp-content/mu-plugins/ai-common.php

@@ -28,6 +28,9 @@ if (defined('SMTP_HOST')) {
 		$phpmailer->SMTPSecure = SMTP_SECURE;
 		$phpmailer->From       = SMTP_FROM;
 		$phpmailer->FromName   = SMTP_NAME;
+		// Do not attempt STARTTLS even if the
+		// server offers it - use SMTPSecure instead.
+		$phpmailer->SMTPAutoTLS = false;
 	}
 }