> Also noticed that I got several ok'ed messages from the server with the
>  following errors:
>
> An error  occurred while processing file  97353 from
>  [log in to unmask]:
> "Mail message sent to the LISTSERV address contains invalid RFC822 fields
>  and
> could not be parsed successfully".
>
> RFC822 parser messages follow:
>
> <W> MESSAGE-ID field duplicated. Last occurrence was retained.
>
> I have seen this error before, and have not been able to determine what is
>  causing it?

It means that there are two Message-ID headers in the message.
Message-ID is used to provide a unique identification code for a
message, so that it can be referenced by other messages.  LISTSERV
complains even when the two message-ids are identical (as usually seems
to be the case when I see it).