Emitter: Send e-mail only on repeated backup fails

hosts/Emitter.nix

@@ -131,7 +131,11 @@
         };
         serviceConfig = {
             Restart = "on-failure";
+
             RestartSec = retryDelay;
+            # Skip transitions through failed state, i.e. don’t send a e-mail
+            # before the maximum number of retries is exhausted
+            RestartMode = "direct";
         };
     };