diff --git a/wp-content/mu-plugins/ai-common.php b/wp-content/mu-plugins/ai-common.php
index 11b9fdee4cf7801b90bc72d70ba3269f1de32141..98d8f680d74f6334087aebf8cef097c9a79e200b 100644
--- a/wp-content/mu-plugins/ai-common.php
+++ b/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;
 	}
 }