+ message_id = notmuch_message_get_message_id (message);
+
+ if (output_format == DUMP_FORMAT_BATCH_TAG &&
+ strchr (message_id, '\n')) {
+ /* This will produce a line break in the output, which
+ * would be difficult to handle in tools. However, it's
+ * also impossible to produce an email containing a line
+ * break in a message ID because of unfolding, so we can
+ * safely disallow it. */
+ fprintf (stderr, "Warning: skipping message id containing line break: \"%s\"\n", message_id);
+ notmuch_message_destroy (message);
+ continue;
+ }