extern BOOL system_filter_uid_set; /* TRUE if uid set */
extern BOOL system_filtering; /* TRUE when running system filter */
+extern BOOL tcp_fastopen_ok; /* appears to be supported by kernel */
extern BOOL tcp_nodelay; /* Controls TCP_NODELAY on daemon */
#ifdef USE_TCP_WRAPPERS
extern uschar *tcp_wrappers_daemon_name; /* tcpwrappers daemon lookup name */