+#if __FreeBSD__ >= 10
+# define LIBICONV_PLUG
+#endif
+/* for more specific version constraints, include <sys/param.h> and look at
+ * __FreeBSD_version */
+
+
+/* When using DKIM, setting OS_SENDFILE can increase
+performance on outgoing mail a bit. */
+
+#define OS_SENDFILE
+extern ssize_t os_sendfile(int, int, off_t *, size_t);