+
+ $mime->header_set('To', 'u@example.com');
+ $mime->header_set('References', '<hello> <world> <n> <u@example.com>');
+ is_deeply(references($mime->header_obj), [qw(hello world)]);
+
+ is_deeply([qw(helloworld alt-id-for-nntp)],
+ mids_for_index($mime->header_obj),
+ 'X-Alt-Message-ID can be indexed');