FUTATSUKI Yasuhito

Per [RFC8601 Sec 2.7.1.](https://www.rfc-editor.org/rfc/rfc8601#section-2.7.1), it seems that we should use `dkim=policy` in such a case. I'll comment it to issue #233 and make a PR.

I glanced the code, then it seems opendkim does not create statistics file, but fopen with "a" (append) in [dkimf_stats_record() in opendkim/stats.c](https://github.com/trusteddomainproject/OpenDKIM/blob/551ab3820476234def82eb2223ca6c7b45b45076/opendkim/stats.c#L124). Also it reports on failure by using syslog...

> ... it seems opendkim does not create statistics file, but ... I'm sorry, mode "a" in fopen(3) create the file if it does not exist.

At least for paths, to convert C string into Python str object, it can be used `PyUnicode_DecodeFSDefault()` as [`to_path()` in `src/utils.h`](https://github.com/libgit2/pygit2/blob/master/src/utils.h#L46) (, and I'm happy if its errors handler is...

While I tried to blame a file, which file name is not valid UTF-8 sequence in bytes, on environment `sys.getfilesystemencoding() == 'utf-8'`, by passing str filename encoded with `encoding='utf-8'` and...

> ... although it still need that caller should handle the error properly. Now it check if the db supports `dkimf_db_walk` operation before calling it.

To correct commit message, I'll rebase and force push it.

> To correct commit message, I'll rebase and force push it. done.

It seems the issue was already fixed in develop branch in https://github.com/trusteddomainproject/OpenARC/commit/495aff78c7e18289eb9182f2bbefd9ee66364346