Add optional inbound relay (backup-MX) behind INBOUND_RELAY_ENABLE.

Port 25 accepts only configured domains and listed recipients, then forwards to an upstream; the outbound path is unchanged when the flag is off.

Co-authored-by: Cursor <cursoragent@cursor.com>

internal/web/handlers/handlers_domains.go

@@ -172,6 +172,13 @@ func (h *Handlers) HandleReload(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, "reload failed", http.StatusInternalServerError)
 		return
 	}
+	if h.cfg.InboundEnabled && h.inbound != nil {
+		if err := h.inbound.Resync(); err != nil {
+			logf("panel: manual reload (inbound): %v", err)
+			http.Error(w, "reload failed", http.StatusInternalServerError)
+			return
+		}
+	}
 	http.Redirect(w, r, "/status?reloaded=1", http.StatusSeeOther)
 }