+/* message_id.h -- construct the body of a Message-ID or Content-ID.
+ *
+ * This code is Copyright (c) 2017, by the authors of nmh. See the
+ * COPYRIGHT file in the root directory of the nmh distribution for
+ * complete copyright information.
+ */
+
+/* What style to use for generated Message-ID and Content-ID header
+ * fields. The localname style is pid.time@localname, where time is
+ * in seconds. The random style replaces the localname with some
+ * (pseudo)random bytes and uses microsecond-resolution time. */
+int save_message_id_style(const char *value);
+
+char *message_id(time_t tclock, int content_id);