DKIM test

[Greg Troxel]

My own message failed DKIM when it arrived back.  Luckily I had the bits
that went out and could diff them.  Multiple interesting things:

   - multiline headers (e.g. References) have modified continuation line
     indentation (plus my local X-Draft-From which was likely not sent):

         References: <aHARwLYKZsegk4OA at oli> <000201dbf1d2$91a4bb80$b4ee3280$@pcorp.us>
        -       <aHAa5Zkb9iA4Q7Sb at oli> <000601dbf1d6$63b9d4e0$2b2d7ea0$@pcorp.us>
        -       <aHAi5-_3NzTD_7Xi at oli>
        -X-Draft-From: ("nnimap+work.lexort.com:lists.osgeo" 1920)
        + <aHAa5Zkb9iA4Q7Sb at oli> <000601dbf1d6$63b9d4e0$2b2d7ea0$@pcorp.us>
        + <aHAi5-_3NzTD_7Xi at oli>

   - extra newline
     The received message had a spurious trailing newline; my message
     had one newline at the end of 'time to time.'  The received message
     had two newlines

   - missing CC: in received copy (and also shows a second continuation
     line indent change)

         From: Greg Troxel <gdt at lexort.com>
         To: Sandro Santilli via Sac <sac at lists.osgeo.org>
        -Cc: Regina Obe <lr at pcorp.us>
         Subject: Re: DKIM test
         In-Reply-To: <aHAi5-_3NzTD_7Xi at oli> (Sandro Santilli via Sac's message of
        -       "Thu, 10 Jul 2025 22:30:31 +0200")
        + "Thu, 10 Jul 2025 22:30:31 +0200")

     but note that my DKIM signature includes cc

so DKIM failures could be caused by any of this.   perhaps blank lines
don't count, and whitespace is canonicalized.   But it could explain
how using cc results in a failure.

It's hard to believe we're the only ones trying to make mailman work.