Allow SMTP servers without auth

server/log.go

@@ -31,7 +31,7 @@ const (
 )
 
 var (
-	normalErrorCodes       = []int{http.StatusNotFound, http.StatusBadRequest, http.StatusTooManyRequests, http.StatusUnauthorized, http.StatusInsufficientStorage}
+	normalErrorCodes       = []int{http.StatusNotFound, http.StatusBadRequest, http.StatusTooManyRequests, http.StatusUnauthorized, http.StatusForbidden, http.StatusInsufficientStorage}
 	rateLimitingErrorCodes = []int{http.StatusTooManyRequests, http.StatusRequestEntityTooLarge}
 )