Comment 4 for bug 1954573

I looked around in the code located at /usr/lib/python3/dist-packages/dkimpy_milter and /usr/lib/python3/dist-packages/dkim.
Specifically the file dkimpy_milter/__init__.py contains the following line:

    syslog.syslog("check_dkim: Internal program fault while verifying: {0}".format(x))

Because the output in syslog said "check_dkim: Internal program fault while verifying: 0" I wondered how the exception could be translated to "(0)", so I added the following line after that

    syslog.syslog(repr(x))

Which gave me the following output: "KeyError(0)"

Not sure if this is a legit way of debugging. I figured the 0 pointed to the first DKIM header in the mail, not sure though. I couldn't really follow the rest of the code, so I left it at that and entered the bug report.
Apologies for omitting this info, there's probably more I'm forgetting to report :(

Update: one more thing I forgot. I'm using postfix. Used the following based on the readme to configure it:

    smtps inet n - - - - smtpd
        ...
        -o smtpd_milters=inet:127.0.0.1:8892
        -o milter_macro_daemon_name=VERIFYING
        ...

    submission inet n - - - - smtpd
        ...
        -o milter_macro_daemon_name=ORIGINATING
        -o smtpd_milters=inet:127.0.0.1:8892
        ...

Signing of outgoing messages seems to work fine, both rsa and ed25519.